Display device

ABSTRACT

A touch panel which is thin, has a simple structure, or is easily incorporated into an electronic device is provided. The touch panel includes a first substrate, a second substrate, a first conductive layer, a second conductive layer, a third conductive layer, a fourth conductive layer, liquid crystal, and an FPC. The first conductive layer has a function of a pixel electrode. The second conductive layer has a function of a common electrode. The third and fourth conductive layers each have a function of an electrode of a touch sensor. The FPC is electrically connected to the fourth conductive layer. The first, second, third, and fourth conductive layers and the liquid crystal are provided between the first and second substrates. The first, second, and third conductive layers are provided over the first substrate. The FPC is provided over the first substrate.

TECHNICAL FIELD

One embodiment of the present invention relates to an input device. Oneembodiment of the present invention relates to a display device. Oneembodiment of the present invention relates to an input/output device.One embodiment of the present invention relates to a touch panel.

Note that one embodiment of the present invention is not limited to theabove technical field. One embodiment of the invention disclosed in thisspecification and the like relates to an object, a method, or amanufacturing method. One embodiment of the present invention relates toa process, a machine, manufacture, or a composition of matter.Specifically, examples of the technical field of one embodiment of thepresent invention disclosed in this specification and the like include asemiconductor device, a display device, a light-emitting device, a powerstorage device, a memory device, an electronic device, a lightingdevice, an input device, an input/output device, a driving methodthereof, and a manufacturing method thereof.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A semiconductor element such as a transistor, asemiconductor circuit, an arithmetic device, and a memory device areeach an embodiment of a semiconductor device. An imaging device, adisplay device, a liquid crystal display device, a light-emittingdevice, an input device, an input/output device, an electro-opticaldevice, a power generation device (including a thin film solar cell, anorganic thin film solar cell, and the like), and an electronic devicemay each include a semiconductor device.

BACKGROUND ART

In recent years, a display device (or a display module) that is providedwith a touch sensor as a position-input means has been put to practicaluse. A display device (or a display module) that is provided with atouch sensor is called a touch panel, a touch screen, or the like(hereinafter, this type of display device may be simply referred to as atouch panel). A device which does not include a display device andincludes only a touch sensor is also called a touch panel in some cases.A display device that is provided with a touch sensor is also called atouch sensor equipped display device, a display device equipped touchpanel, a display module, or the like in some cases. Furthermore, adisplay device in which a touch sensor is incorporated is called anin-cell touch sensor (or an in-cell touch sensor equipped displaydevice), an on-cell touch sensor (or an on-cell touch sensor equippeddisplay device), or the like in some cases. In the in-cell touch sensor,for example, an electrode used for a liquid crystal element is also usedas an electrode for the touch sensor. In the on-cell touch sensor, forexample, an electrode for the touch sensor is formed on the upper side(the side that is not provided with a display element) of a countersubstrate. Examples of a portable information terminal provided withsuch a touch panel or the like include a smartphone and a tabletterminal.

As one of display devices, there is a liquid crystal display deviceprovided with a liquid crystal element. For example, an active matrixliquid crystal display device in which pixel electrodes are arranged ina matrix and transistors are used as switching elements connected torespective pixel electrodes has attracted attention.

For example, active matrix liquid crystal display devices in which atransistor formed using a metal oxide for a channel formation region isused as each of switching elements connected to respective pixelelectrodes are known (see Patent Documents 1 and 2).

Touch panels in which a liquid crystal element is used are disclosed inPatent Documents 3 to 6.

It is known that liquid crystal display devices are roughly divided intotwo kinds of liquid crystal display devices: a transmissive liquidcrystal display device and a reflective liquid crystal display device.

In the transmissive liquid crystal display device, a backlight such as acold cathode fluorescent lamp or an LED is used, and optical modulationaction of liquid crystal is utilized to select one of the two states: astate where light from the backlight passes through liquid crystal to beoutput to the outside of the liquid crystal display device and a statewhere light is not output to the outside of the liquid crystal displaydevice, whereby a bright or dark image is displayed. Furthermore, thoseimages are combined to perform image display.

In the reflective liquid crystal display device, optical modulationaction of liquid crystal is utilized to select one of the two states: astate where external light, that is, incident light is reflected on apixel electrode to be output to the outside of the device and a statewhere incident light is not output to the outside of the device, wherebya bright or dark image is displayed. Furthermore, those images arecombined to perform image display.

REFERENCE Patent Documents

[Patent Document 1] Japanese Published Patent Application No.2007-123861

[Patent Document 2] Japanese Published Patent Application No.2007-096055

[Patent Document 3] Japanese Published Patent Application No.2011-197685

[Patent Document 4] Japanese Published Patent Application No.2014-044537

[Patent Document 5] Japanese Published Patent Application No.2014-178847

[Patent Document 6] U.S. Pat. No. 7,920,129

DISCLOSURE OF INVENTION

What is desirable is a touch panel in which a display panel (a displaydevice or a display module) is provided with a function of inputtingdata with a finger, a stylus, or the like touching a screen as a userinterface.

Furthermore, it is required that an electronic device using a touchpanel is reduced in thickness and weight. Therefore, a touch panelitself is required to be reduced in thickness and weight.

For example, in a touch panel, a touch sensor can be provided on theviewer side (the display surface side), that is, the side a finger or apen (stylus) touches, of a display panel.

For example, in a touch panel (or a display module), a substrateprovided with a touch sensor can be attached to the display surface sideof a display panel. In other words, in a touch panel (or a displaymodule), a display panel and a touch sensor can be separate componentsand can be attached to each other. However, in such a structure, asubstrate for a touch sensor is needed in addition to a substrate for adisplay panel, resulting in that the thickness of a touch panel (or adisplay module) cannot be reduced and the number of components isincreased.

An object of one embodiment of the present invention is to provide athin touch panel (or a thin touch sensor equipped display device) andthe like. Another object is to provide a touch panel (or a touch sensorequipped display device) with a simple structure and the like. Anotherobject is to provide a touch panel (or a touch sensor equipped displaydevice) which can be easily incorporated into an electronic device andthe like. Another object is to provide a touch panel (or a touch sensorequipped display device) with a small number of components and the like.Another object is to provide a lightweight touch panel (or a lightweighttouch sensor equipped display device) and the like.

Another object is to provide a novel input device. Another object is toprovide a novel input/output device. Another object is to provide anovel display device. Note that the description of these objects doesnot disturb the existence of other objects. In one embodiment of thepresent invention, there is no need to achieve all the objects. Otherobjects will be apparent from and can be derived from the description ofthe specification, the drawings, the claims, and the like.

One embodiment of the present invention is a touch panel including afirst substrate, a second substrate, a first conductive layer, a secondconductive layer, a third conductive layer, a fourth conductive layer,liquid crystal, and an FPC. The first conductive layer has a function ofa pixel electrode. The second conductive layer has a function of acommon electrode. The third conductive layer and the fourth conductivelayer each have a function of an electrode of a touch sensor. The FPC iselectrically connected to the fourth conductive layer. The firstconductive layer, the second conductive layer, the third conductivelayer, the fourth conductive layer, and the liquid crystal are providedbetween the first substrate and the second substrate. The firstconductive layer, the second conductive layer, and the third conductivelayer are provided over the first substrate. The FPC is provided overthe first substrate.

It is preferable that the above-described touch panel further include afifth conductive layer and a connector, the fifth conductive layer beprovided over the first substrate, the fourth conductive layer beprovided over the second substrate, and the fourth conductive layer andthe fifth conductive layer be electrically connected to each otherthrough the connector.

It is preferable that the fourth conductive layer be provided over thefirst substrate.

It is preferable that one of the third conductive layer and the fourthconductive layer be provided on the same plane as the second conductivelayer.

It is preferable that the third conductive layer be provided on the sameplane as the first conductive layer or the second conductive layer andthat the fourth conductive layer be provided on the same plane as thefirst conductive layer or the second conductive layer.

It is preferable that the second conductive layer and one of the thirdconductive layer and the fourth conductive layer be continuous.

It is preferable that the first conductive layer and one of the thirdconductive layer and the fourth conductive layer be continuous.

In accordance with one embodiment of the present invention, a thin touchpanel (or a thin touch sensor equipped display device) and the like canbe provided. A touch panel (or a touch sensor equipped display device)with a simple structure and the like can be provided. A touch panel (ora touch sensor equipped display device) which can be easily incorporatedinto an electronic device and the like can be provided. A touch panel(or a touch sensor equipped display device) with a small number ofcomponents and the like can be provided. A lightweight touch panel (or alightweight touch sensor equipped display device) and the like can beprovided. A novel input device can be provided. A novel input/outputdevice can be provided. A novel display device can be provided. Notethat the description of these effects does not disturb the existence ofother effects. One embodiment of the present invention does notnecessarily achieve all the effects listed above. Other effects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are a block diagram and a timing chart of a touch sensorof one embodiment.

FIGS. 2A and 2B illustrate pixels each provided with a touch sensor ofone embodiment.

FIG. 3 illustrates pixels each provided with a touch sensor of oneembodiment.

FIG. 4 illustrates pixels each provided with a touch sensor of oneembodiment.

FIG. 5 illustrates pixels each provided with a touch sensor of oneembodiment.

FIGS. 6A to 6C illustrate operation of a touch sensor and a pixel of oneembodiment.

FIGS. 7A to 7E illustrate structure examples of a touch panel of oneembodiment.

FIGS. 8A to 8C illustrate structure examples of a touch panel of oneembodiment.

FIG. 9 illustrates a structure example of a touch panel of oneembodiment.

FIGS. 10A and 10B illustrate structure examples of a touch panel of oneembodiment.

FIGS. 11A to 11C illustrate structure examples of a touch panel of oneembodiment.

FIG. 12 illustrates a structure example of a touch panel of oneembodiment.

FIGS. 13A and 13B illustrate structure examples of a touch panel of oneembodiment.

FIG. 14 illustrates a structure example of a touch panel of oneembodiment.

FIGS. 15A to 15C illustrate structure examples of a touch panel of oneembodiment.

FIGS. 16A to 16C illustrate structure examples of a touch panel of oneembodiment.

FIGS. 17A and 17B illustrate structure examples of a touch panel of oneembodiment.

FIGS. 18A and 18B illustrate a structure example of a touch panel of oneembodiment.

FIG. 19 illustrates a structure example of a touch panel of oneembodiment.

FIG. 20 illustrates a structure example of a touch panel of oneembodiment.

FIG. 21 illustrates a structure example of a touch panel of oneembodiment.

FIG. 22 illustrates a structure example of a touch panel of oneembodiment.

FIG. 23 illustrates a structure example of a touch panel of oneembodiment.

FIG. 24 illustrates a structure example of a touch panel of oneembodiment.

FIG. 25 illustrates a structure example of a touch panel of oneembodiment.

FIG. 26 illustrates a structure example of a touch panel of oneembodiment.

FIG. 27 illustrates a structure example of a touch panel of oneembodiment.

FIG. 28 illustrates a structure example of a touch panel of oneembodiment.

FIG. 29 illustrates a structure example of a touch panel of oneembodiment.

FIG. 30 illustrates a structure example of a touch panel of oneembodiment.

FIG. 31 illustrates a structure example of a touch panel of oneembodiment.

FIG. 32 illustrates a structure example of a touch panel of oneembodiment.

FIG. 33 illustrates a structure example of a touch panel of oneembodiment.

FIG. 34 illustrates a structure example of a touch panel of oneembodiment.

FIG. 35 illustrates a structure example of a touch panel of oneembodiment.

FIG. 36 illustrates a structure example of a touch panel of oneembodiment.

FIG. 37 illustrates a structure example of a touch panel of oneembodiment.

FIG. 38 illustrates a structure example of a touch panel of oneembodiment.

FIG. 39 illustrates a structure example of a touch panel of oneembodiment.

FIG. 40 illustrates a structure example of a touch panel of oneembodiment.

FIG. 41 illustrates a structure example of a touch panel of oneembodiment.

FIG. 42 illustrates a structure example of a touch panel of oneembodiment.

FIG. 43 illustrates a structure example of a touch panel of oneembodiment.

FIG. 44 illustrates a structure example of a touch panel of oneembodiment.

FIG. 45 illustrates a structure example of a touch panel of oneembodiment.

FIG. 46 illustrates a structure example of a touch panel of oneembodiment.

FIG. 47 illustrates a structure example of a touch panel of oneembodiment.

FIG. 48 illustrates a structure example of a touch panel of oneembodiment.

FIG. 49 illustrates a structure example of a touch panel of oneembodiment.

FIG. 50 illustrates a structure example of a touch panel of oneembodiment.

FIG. 51 illustrates a structure example of a touch panel of oneembodiment.

FIG. 52 illustrates a structure example of a touch panel of oneembodiment.

FIG. 53 illustrates a structure example of a touch panel of oneembodiment.

FIG. 54 illustrates a structure example of a touch panel of oneembodiment.

FIG. 55 illustrates a structure example of a touch panel of oneembodiment.

FIG. 56 illustrates a structure example of a touch panel of oneembodiment.

FIG. 57 illustrates a structure example of a touch panel of oneembodiment.

FIG. 58 illustrates a structure example of a touch panel of oneembodiment.

FIG. 59 illustrates a structure example of a touch panel of oneembodiment.

FIG. 60 illustrates a structure example of a touch panel of oneembodiment.

FIG. 61 illustrates a structure example of a touch panel of oneembodiment.

FIG. 62 illustrates a structure example of a touch panel of oneembodiment.

FIG. 63 illustrates a structure example of a touch panel of oneembodiment.

FIG. 64 illustrates a structure example of a touch panel of oneembodiment.

FIG. 65 illustrates a structure example of a touch panel of oneembodiment.

FIG. 66 illustrates a structure example of a touch panel of oneembodiment.

FIG. 67 illustrates a structure example of a touch panel of oneembodiment.

FIG. 68 illustrates a structure example of a touch panel of oneembodiment.

FIG. 69 illustrates a structure example of a touch panel of oneembodiment.

FIG. 70 illustrates a structure example of a touch panel of oneembodiment.

FIG. 71 illustrates a structure example of a touch panel of oneembodiment.

FIG. 72 illustrates a structure example of a touch panel of oneembodiment.

FIG. 73 illustrates a structure example of a touch panel of oneembodiment.

FIG. 74 illustrates a structure example of a touch panel of oneembodiment.

FIG. 75 illustrates a structure example of a touch panel of oneembodiment.

FIG. 76 illustrates a structure example of a touch panel of oneembodiment.

FIG. 77 illustrates a structure example of a touch panel of oneembodiment.

FIG. 78 illustrates a structure example of a touch panel of oneembodiment.

FIG. 79 illustrates a structure example of a touch panel of oneembodiment.

FIGS. 80A and 80B are schematic views each illustrating an example of adisplay device.

FIGS. 81A1, 81A2, 81B1, 81B2, 81C1, and 81C2 are cross-sectional viewseach illustrating one embodiment of a transistor.

FIGS. 82A1, 82A2, 82A3, 82B1, and 82B2 are cross-sectional views eachillustrating one embodiment of a transistor.

FIGS. 83A1, 83A2, 83A3, 83B1, 83B2, 83C1, and 83C2 are cross-sectionalviews each illustrating one embodiment of a transistor.

FIGS. 84A to 84C are a plan view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 85A to 85C are a plan view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 86A to 86C are a plan view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 87A to 87C are a plan view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 88A to 88C are a plan view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 89A and 89B each show an energy band structure.

FIG. 90 illustrates a display module of one embodiment.

FIGS. 91A to 91H each illustrate an electronic device of one embodiment.

FIGS. 92A and 92B each illustrate an electronic device of oneembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to the drawings.Note that the present invention is not limited to the description below,and it is easily understood by those skilled in the art that the modeand details can be variously changed without departing from the spiritand scope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and the description of suchportions is not repeated. Furthermore, the same hatching pattern isapplied to portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing referred to in this specification, the size,the layer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, embodiments of the present inventionare not limited to such a scale.

In this specification and the like, ordinal numbers such as “first” and“second” are used in order to avoid confusion among components and donot limit the components numerically.

Note that the terms “film” and “layer” can be interchanged with eachother in some cases. For example, in some cases, the term “conductivefilm” can be used instead of the term “conductive layer”, and the term“insulating layer” can be used instead of the term “insulating film”.

Embodiment 1

In this embodiment, a driving method, a mode, and a structure example ofan input device or an input/output device of one embodiment of thepresent invention will be described with reference to the drawings.

Example of Sensing Method of Sensor

FIG. 1A is a block diagram illustrating the structure of a mutualcapacitive touch sensor. FIG. 1A illustrates a pulse voltage outputcircuit 601 and a current sensing circuit 602. In FIG. 1A, as anexample, six wirings X1 to X6 represent electrodes 621 to which a pulsevoltage is applied, and six wirings Y1 to Y6 represent electrodes 622that sense changes in current. The number of such electrodes is notlimited to those illustrated in this example. FIG. 1A also illustrates acapacitor 603 that is formed with the electrodes 621 and 622 overlappingwith each other or being provided very close to each other. Note thatthe functions of the electrodes 621 and 622 can be interchanged witheach other.

The pulse voltage output circuit 601 is, for example, a circuit forsequentially applying a pulse voltage to the wirings X1 to X6. Byapplying a pulse voltage to the wirings X1 to X6, an electric field isgenerated between the electrodes 621 and 622 of the capacitors 603. Witha pulse voltage, current flows through the capacitor 603. An electricfield generated between the electrodes 621 and 622 is changed by beingblocked, for example, when a finger or a stylus touches the touchsensor. That is, for example, by touch with a finger or a stylus, thecapacitance of the capacitor 603 is changed. By utilizing the change incapacitance caused by touch with a finger or a stylus as describedabove, the approach or contact of an object can be detected.

The current sensing circuit 602 is a circuit for sensing changes incurrent flowing through the wirings Y1 to Y6 that are caused by thechanges in capacitance of the capacitors 603. No change in the currentvalues of the wirings Y1 to Y6 is sensed when there is no approach orcontact of an object, whereas a decrease in the current value is sensedwhen capacitance is decreased owing to the approach or contact of anobject. In order to sense a change in current, the total amount ofcurrent may be sensed. In that case, an integrator circuit or the likemay be used for sensing the total amount of current. Alternatively, thepeak value of current may be sensed. In that case, current may beconverted into voltage, and the peak value of voltage may be sensed.

FIG. 1B is a timing chart showing input and output waveforms of themutual capacitive touch sensor illustrated in FIG. 1A. In FIG. 1B,detection of an object is performed in all the rows and columns in oneframe period. FIG. 1B shows a period during which an object is notdetected (not touched) and a period during which an object is detected(touched). Sensed current values of the wirings Y1 to Y6 are shown aswaveforms of voltage values. Note that a display panel performs displayoperation. The timing of the display operation in the display panel ispreferably in synchronization with the timing of the sensing operationin the touch sensor. FIG. 1B shows an example in which these timings arenot in synchronization.

A pulse voltage is sequentially applied to the wirings X1 to X6, and thewaveforms of the wirings Y1 to Y6 change in accordance with the pulsevoltage. When there is no approach or contact of an object, thewaveforms of the wirings Y1 to Y6 change in accordance with changes inthe voltages of the wirings X1 to X6. In contrast, the current value isdecreased at the point of approach or contact of an object; accordingly,the waveform of the voltage value also changes.

By sensing a change in capacitance in this manner, the approach orcontact of an object can be detected. Even when an object such as afinger or a stylus does not touch but only approaches a touch sensor ora touch panel, a signal may be sensed in some cases.

It is preferable that, as an example, the pulse voltage output circuit601 and the current sensing circuit 602 be formed in one IC chip. Forexample, the IC chip is preferably mounted on a touch panel or asubstrate in a housing of an electronic device. In the case where thetouch panel has flexibility, parasitic capacitance might be increased ina bent portion of the touch panel, and the influence of noise might beincreased. In view of this, it is preferable to use an IC chip to whicha driving method less influenced by noise is applied. For example, it ispreferable to use an IC chip to which a driving method capable ofincreasing a signal-noise ratio (S/N ratio) is applied.

Although FIG. 1A illustrates, as a touch sensor, the structure of apassive matrix touch sensor in which only the capacitor 603 is providedat the intersection of wirings, an active matrix touch sensor includinga transistor and a capacitor may also be used.

Structure Example of In-Cell Touch Panel

An example in which at least one of electrodes included in a touchsensor is formed over a substrate provided with a display element, atransistor, and the like is described below.

A structure example of a touch panel incorporating a touch sensor into adisplay portion including a plurality of pixels (i.e., an in-cell touchpanel) is described below. An example in which a liquid crystal elementis used as a display element provided in the pixel is described.However, one embodiment of the present invention is not limited thereto,and any of various display elements can be used.

FIG. 2A is an equivalent circuit diagram of part of a pixel circuitprovided in a display portion of a touch panel in this structureexample.

Each pixel includes at least a transistor 63 and a liquid crystalelement 64. Each pixel further includes a storage capacitor in somecases. A gate of the transistor 63 is electrically connected to a wiring61, and one of a source and a drain of the transistor 63 is electricallyconnected to a wiring 62.

The pixel circuit includes a plurality of wirings extending in the Xdirection (e.g., a wiring 72_1 and a wiring 72_2) and a plurality ofwirings extending in the Y direction (e.g., a wiring 71_1 and a wiring71_2). They are provided to intersect with each other, and capacitanceis formed therebetween.

For example, among the pixels provided in the pixel circuit, electrodeson one side of liquid crystal elements of some pixels adjacent to eachother are electrically connected to each other to form one block. Forexample, a plurality of linear blocks extending in the Y direction(e.g., a block 65_1 and a block 65_2) are formed. Although only part ofthe pixel circuit is illustrated in FIG. 2A, these blocks are repeatedlyarranged in the X direction. An electrode on one side of the liquidcrystal element is a common electrode or a counter electrode, forexample. An electrode on the other side of the liquid crystal elementis, for example, a pixel electrode.

With the above structure, the electrode on one side of the liquidcrystal element in the pixel circuit can also serve as an electrodeincluded in a touch sensor. In FIG. 2A, the wirings 71_1 and 71_2 eachserve as the electrode included in the touch sensor as well as theelectrode on one side of the liquid crystal element. In contrast, thewirings 72_1 and 72_2 each function as an electrode included in thetouch sensor. In this manner, the structure of the touch panel can besimplified. Although the plurality of wirings extending in the Ydirection (e.g., the wirings 71_1 and 71_2) each serve as the electrodeincluded in the touch sensor as well as the electrode on one side of theliquid crystal element in FIG. 2A, one embodiment of the presentinvention is not limited thereto. For example, the plurality of wiringsextending in the X direction (e.g., the wirings 72_1 and 72_2) may eachserve as the electrode included in the touch sensor as well as theelectrode on one side of the liquid crystal element. An example of acircuit diagram in that case is shown in FIG. 3 .

Although FIG. 2A and FIG. 3 each illustrate the example in which onewiring serves as the electrode included in the touch sensor as well asthe electrode on one side of the liquid crystal element, one embodimentof the present invention is not limited to this example. The electrodeon one side of the liquid crystal element and the electrode included inthe touch sensor may be formed with separate wirings. For example, asillustrated in FIG. 2B, the electrodes on one side of the liquid crystalelements 64 may be electrically connected to a wiring 66. When at leastone of the wiring 66, the electrode on one side of the liquid crystalelement 64, and the electrode on the other side of the liquid crystalelement 64 and at least one of a wiring extending in the X direction anda wiring extending in the Y direction are formed by processing the sameconductive film at the same time, the manufacturing process of the touchpanel can be simplified. For example, the wiring 66, the wiring 71_1,and the wiring 71_2 may be formed at the same time. Alternatively, thewiring 66, the wiring 72_1, and the wiring 72_2 may be formed at thesame time.

Although FIGS. 2A and 2B and FIG. 3 each illustrate the example in whichthe liquid crystal element is used as a display element, one embodimentof the present invention is not limited thereto. FIG. 4 and FIG. 5 eachillustrate an example in which a light-emitting element is used as adisplay element.

FIG. 6A is an equivalent circuit diagram illustrating the connectionbetween a plurality of wirings 72 extending in the X direction and aplurality of wirings 71 extending in the Y direction. In the circuitdiagram, the touch sensor is a projected mutual capacitive touch sensor.Input voltage (or selection voltage) or a common potential (or a groundpotential or a reference potential) can be input to each of the wirings71 extending in the Y direction. A ground potential (or a referencepotential) can be input to each of the wirings 72 extending in the Xdirection, or the wirings 72 can be electrically connected to a sensingcircuit. Note that the wirings 71 and the wirings 72 can be interchangedwith each other. That is, the wirings 71 can be electrically connectedto the sensing circuit.

Operation of the above-described touch panel is described below withreference to FIGS. 6B and 6C.

For example, one frame period is divided into a writing period and asensing period. The writing period is a period during which image datais written to a pixel and the wirings 61 in FIGS. 2A and 2B and the like(also referred to as gate lines or scan lines) are sequentiallyselected. The sensing period is a period during which sensing isperformed by the touch sensor and the wirings 71 extending in the Ydirection are sequentially selected and input voltage is input.

FIG. 6B is an equivalent circuit diagram in the writing period. In thewiring period, a common potential is input to both the wirings 72extending in the X direction and the wirings 71 extending in the Ydirection.

FIG. 6C is an equivalent circuit diagram at some point in time in thesensing period. In the sensing period, each of the wirings 72 extendingin the X direction is electrically connected to the sensing circuit.Input voltage is input to the wirings 71 extending in the Y directionwhich are selected, and a common potential is input to the wirings 71extending in the Y direction which are not selected.

Note that the driving method described here can be applied not only tothe in-cell touch panel but also to the above-described touch panel.

It is preferable that the period during which an image is written andthe period during which sensing is performed by the touch sensor beseparately provided as described above. For example, sensing ispreferably performed in a blanking period. In this manner, a decrease insensitivity of the touch sensor caused by noise generated when an imageis written to a pixel can be suppressed.

Examples of Touch Panel

Examples of a touch panel of one embodiment of the present invention aredescribed below.

Note that in this specification and the like, a touch panel has afunction of displaying or outputting an image or the like on or to adisplay surface and a function of a touch sensor capable of detectingthe approach or contact of an object such as a finger or a stylus to thedisplay surface. Therefore, the touch panel is one embodiment of aninput/output device.

In this specification and the like, a structure in which a connectorsuch as a flexible printed circuit (FPC) or a tape carrier package (TCP)is attached to a substrate of a touch panel, or a structure in which anintegrated circuit (IC) is mounted on a substrate by a chip on glass(COG) method is referred to as a touch panel module or a display module,or simply referred to as a touch panel in some cases.

A capacitive touch sensor that can be used for one embodiment of thepresent invention includes a pair of conductive layers. Capacitance isformed between the pair of conductive layers. The capacitance betweenthe pair of conductive layers changes when an object touches orapproaches the pair of conductive layers. Utilizing this change,detection can be performed.

Examples of the capacitive touch sensor include a surface capacitivetouch sensor and a projected capacitive touch sensor. Examples of theprojected capacitive touch sensor include a self capacitive touch sensorand a mutual capacitive touch sensor, which differ mainly in the drivingmethod. The use of a mutual capacitive touch sensor is preferablebecause multiple points can be detected simultaneously. Note that theself capacitive touch sensor can also be used.

As a display element in a touch panel of one embodiment of the presentinvention, a variety of display elements, for example, a liquid crystalelement (using a vertical electric field mode or a horizontal electricfield mode), an optical element utilizing micro electro mechanicalsystems (MEMS), a light-emitting element such as an organicelectroluminescence (EL) element or a light-emitting diode (LED), and anelectrophoretic element, can be used.

Here, as an example, a transmissive liquid crystal display deviceincluding a liquid crystal element using a horizontal electric fieldmode as a display element is preferably used for the touch panel.

A touch panel of one embodiment of the present invention includes,between a pair of substrates, a pair of electrodes (also referred to asconductive layers or wirings) included in a touch sensor and thus has astructure in which a display panel and the touch sensor are combined.That is, the touch sensor is not formed over another substrate or thelike but between the pair of substrates provided with a display elementand a transistor. Therefore, the thickness of the touch panel isreduced, leading to a lightweight touch panel.

In addition, in the touch panel of one embodiment of the presentinvention, a flexible printed circuit (FPC) which supplies a signal fordriving a pixel and an FPC which drives the touch sensor are bothprovided over one of the pair of substrates. In this manner, the touchpanel can be easily incorporated into an electronic device, and thenumber of components can be reduced.

FIG. 7A is a cross-sectional schematic view of a touch panel 10 of oneembodiment of the present invention.

The touch panel 10 includes a substrate 11, a substrate 12, an FPC 13, aconductive layer 14, a liquid crystal element 20, a coloring layer 31, aconductive layer 41, and the like.

The liquid crystal element 20 includes a conductive layer 21, aconductive layer 22, and liquid crystal 23. In the example illustratedhere, a liquid crystal element using a fringe field switching (FFS) modeis used as the liquid crystal element 20. The conductive layer 22 ispositioned over the conductive layer 21 with an insulating layerprovided therebetween. For example, the conductive layer 22 has acomb-like top shape or a top shape provided with a slit (a top shape isalso referred to as a planar shape). One of the conductive layers 21 and22 functions as a common electrode, and the other functions as a pixelelectrode. In the case where a light-emitting element or the like isused as a display element, for example, the conductive layer 22 does nothave a comb-like top shape or a top shape provided with a slit.

A touch sensor can perform detection by utilizing the capacitance formedbetween the conductive layer 41 provided on the substrate 12 side andthe conductive layer 21 functioning as one of a pair of electrodes ofthe liquid crystal element 20. In the example illustrated here, theconductive layer 41 is preferably provided on a surface which faces thesubstrate 11 (a lower surface) of the substrate 12.

The conductive layer 41 provided on the substrate 12 side iselectrically connected to the conductive layer 14 provided on thesubstrate 11 side through a connection layer 15. The conductive layer 14is electrically connected to the FPC 13 provided on the substrate 11side. With such a structure, an FPC which drives the touch sensor and anFPC which drives the liquid crystal element 20 can both be provided overone substrate.

In the case where, for example, the conductive layer functioning as theelectrode of the touch sensor is provided on a surface which does notface the substrate 11 (an upper surface) of the substrate 12 in thetouch panel, an FPC electrically connected to the conductive layer isnecessarily attached to the substrate 12. In addition, when theconnection layer 15 illustrated in FIG. 7A is not used, the FPCelectrically connected to the conductive layer 41 needs to be attachedto the substrate 12. Furthermore, when the conductive layer functioningas the electrode of the touch sensor is provided over a substrate whichis not the substrate 11 or the substrate 12, an FPC needs to be attachedto the substrate. With these structures, the number of components mightbe increased or there might be a limitation when the touch panel isincorporated into an electronic device because of the position of theFPC. In one embodiment of the present invention, however, the FPCs canbe attached only to one of the pair of substrates. Therefore, the numberof components can be reduced, leading to a touch panel that is easilyincorporated into an electronic device.

When one of the pair of electrodes of the liquid crystal element 20 alsoserves as at least one of the pair of electrodes included in the touchsensor, the manufacturing process can be simplified, thereby improvingthe yield and reducing the manufacturing cost.

FIG. 7B illustrates an example in which the conductive layer 41functioning as the electrode of the touch sensor is provided on thesubstrate 11 side. The conductive layer 41 is electrically connected tothe conductive layer 14. The touch sensor can perform detection byutilizing the capacitance formed between the conductive layer 41 and theconductive layer 21 functioning as one of the pair of electrodes (e.g.,a common electrode) of the liquid crystal element 20. Also with thisstructure, the FPC 13 can be provided on the substrate 11 side. Asurface on the substrate 11 side is preferably used as a touch surface,because the detection sensitivity of the touch panel can be increased.

FIG. 7C illustrates an example in which the conductive layer 41 isformed on the same plane as the conductive layer 22. The conductivelayer 41 is electrically connected to the conductive layer 14 in aregion which is not illustrated in the drawing. The conductive layer 41and the conductive layer 22 are preferably formed by processing the sameconductive film at the same time. The touch sensor can perform detectionby utilizing the capacitance formed between the conductive layer 41 andthe conductive layer 21. For example, the conductive layer 21 has both afunction of the common electrode of the liquid crystal element 20 and afunction of the electrode of the touch sensor.

FIG. 7D illustrates an example in which the liquid crystal element 20 isa liquid crystal element using an in-plane switching (IPS) mode.

The conductive layers 21 and 22 included in the liquid crystal element20 are provided on the same plane. The conductive layers 21 and 22 eachhave a comb-like shape and are provided so as to be engaged with eachother. The touch sensor can perform detection by utilizing thecapacitance formed between the conductive layer 41 and the conductivelayer 21. For example, the conductive layer 21 has both a function ofthe common electrode of the liquid crystal element 20 and a function ofthe electrode of the touch sensor.

The conductive layer 41 functioning as one electrode of the touch sensoris formed on the same plane as the conductive layers 21 and 22. Theconductive layer 41 is electrically connected to the conductive layer 14in a region which is not illustrated in the drawing. The conductivelayer 41, the conductive layer 21, and the conductive layer 22 arepreferably formed by processing the same conductive film at the sametime.

FIG. 7E illustrates another example in which the liquid crystal element20 is a liquid crystal element using an FFS mode. The touch sensor canperform detection by utilizing the capacitance formed between aconductive layer 41 a and a conductive layer 41 b. One of the conductivelayers 21 and 22 has a function of the common electrode of the liquidcrystal element 20, and the other has a function of the pixel electrodeof the liquid crystal element 20.

The conductive layer 41 a is provided on the same plane as theconductive layer 22. The conductive layer 41 b and the conductive layer21 are provided on the same plane. The conductive layer 41 a and theconductive layer 22 are preferably formed by processing the sameconductive film at the same time. The conductive layer 41 b and theconductive layer 21 are also preferably formed by processing the sameconductive film at the same time. With such a structure, the pair ofelectrodes included in the touch sensor can be formed at the same timeas the pair of electrodes of the liquid crystal element 20. Accordingly,the touch panel 10 having a function of the touch sensor can bemanufactured without increasing the number of manufacturing steps.

FIG. 8A illustrates another example in which the liquid crystal element20 is a liquid crystal element using an FFS mode. The touch sensor canperform detection by utilizing the capacitance formed between theconductive layers 41 a and 41 b. For example, the conductive layer 21has a function of the common electrode of the liquid crystal element 20.

The conductive layers 41 a and 41 b are provided on the same plane asthe conductive layer 22. The conductive layers 41 a and 41 b and theconductive layer 22 are preferably formed by processing the sameconductive film at the same time. With such a structure, the pair ofelectrodes included in the touch sensor can be formed at the same timeas one of the pair of electrodes of the liquid crystal element 20.Accordingly, the touch panel 10 having a function of the touch sensorcan be manufactured without increasing the number of manufacturingsteps.

Although the conductive layer 41 a is provided so as to overlap with theconductive layer 21, one embodiment of the present invention is notlimited thereto. The conductive layer 21 can be provided so as not tooverlap with the conductive layer 41 a. Consequently, parasiticcapacitance due to the conductive layer 41 a can be reduced. In asimilar manner, the conductive layer 21 can be provided so as not to tooverlap with the conductive layer 41 b.

FIG. 8B illustrates another example in which the liquid crystal element20 is a liquid crystal element using an FFS mode. The touch sensor canperform detection by utilizing the capacitance formed between theconductive layers 41 a and 41 b. One of the conductive layers 21 and 22has a function of the common electrode of the liquid crystal element 20,and the other has a function of the pixel electrode of the liquidcrystal element 20.

The conductive layers 41 a and 41 b are provided on the same plane asthe conductive layer 21. The conductive layers 41 a and 41 b and theconductive layer 21 are preferably formed by processing the sameconductive film at the same time. With such a structure, the pair ofelectrodes included in the touch sensor can be formed at the same timeone of the pair of electrodes of the liquid crystal element 20.Accordingly, the touch panel 10 having a function of the touch sensorcan be manufactured without increasing the number of manufacturingsteps.

FIG. 8C illustrates another example in which the liquid crystal element20 is a liquid crystal element using an FFS mode. The touch sensor canperform detection by utilizing the capacitance formed between theconductive layer 41 and the conductive layer 21 functioning as one ofthe pair of electrodes of the liquid crystal element 20. For example,the conductive layer 21 has both a function of the common electrode ofthe liquid crystal element 20 and a function of the electrode of thetouch sensor.

The conductive layer 41 is provided on the same plane as the conductivelayer 21. The conductive layer 41 and the conductive layer 21 arepreferably formed by processing the same conductive film at the sametime. With such a structure, the pair of electrodes included in thetouch sensor can be formed at the same time as one of the pair ofelectrodes of the liquid crystal element 20. Accordingly, the touchpanel 10 having a function of the touch sensor can be manufacturedwithout increasing the number of manufacturing steps.

FIG. 9 illustrates an example in which the liquid crystal element 20 isa liquid crystal element using an IPS mode.

The conductive layers 21 and 22 included in the liquid crystal element20 are provided on the same plane. The conductive layers 21 and 22 eachhave a comb-like shape and are provided so as to be engaged with eachother. One of the conductive layers 21 and 22 has a function of thecommon electrode of the liquid crystal element 20, and the other has afunction of the pixel electrode of the liquid crystal element 20.

The conductive layers 41 a and 41 b functioning as the electrodes of thetouch sensor are formed on the same plane as the conductive layers 21and 22. The conductive layers 41 a and 41 b and the conductive layers 21and 22 are preferably formed by processing the same conductive film atthe same time. The touch sensor can perform detection by utilizing thecapacitance formed between the conductive layers 41 a and 41 b.

By forming the conductive layer 21 of the liquid crystal element usingan FFS mode to have a comb-like top shape or a top shape provided with aslit, a liquid crystal element using an IPS mode can be obtained.

FIG. 10A illustrates an example that is obtained by changing the liquidcrystal element illustrated in FIG. 7C into a liquid crystal elementusing an IPS mode. For example, the conductive layer 21 has both afunction of the common electrode of the liquid crystal element 20 and afunction of the electrode of the touch sensor.

FIG. 10B illustrates an example that is obtained by changing the liquidcrystal element illustrated in FIG. 7E into a liquid crystal elementusing an IPS mode. One of the conductive layers 21 and 22 has a functionof the common electrode of the liquid crystal element 20, and the otherhas a function of the pixel electrode of the liquid crystal element 20.

FIG. 11A illustrates an example that is obtained by changing the liquidcrystal element illustrated in FIG. 8A into a liquid crystal elementusing an IPS mode, and FIG. 11B illustrates an example that is obtainedby changing the liquid crystal element illustrated in FIG. 8B into aliquid crystal element using an IPS mode. One of the conductive layers21 and 22 has a function of the common electrode of the liquid crystalelement 20, and the other has a function of the pixel electrode of theliquid crystal element 20.

FIG. 11C illustrates an example that is obtained by changing the liquidcrystal element illustrated in FIG. 8C into a liquid crystal elementusing an IPS mode. For example, the conductive layer 21 has both afunction of the common electrode of the liquid crystal element 20 and afunction of the electrode of the touch sensor.

In many of the above examples, an upper electrode is the pixel electrodeof the liquid crystal element 20, and a lower electrode is the commonelectrode of the liquid crystal element 20; however, one embodiment ofthe present invention is not limited thereto. The upper electrode can bethe common electrode of the liquid crystal element 20, and the lowerelectrode can be the pixel electrode of the liquid crystal element 20.

FIG. 12 illustrates an example in which an upper electrode in FIG. 7C isused as the common electrode of the liquid crystal element 20. Forexample, the conductive layer 21 has both a function of the commonelectrode of the liquid crystal element 20 and a function of theelectrode of the touch sensor.

FIG. 13A illustrates an example in which an upper electrode in FIG. 8Ais used as the common electrode of the liquid crystal element 20. Forexample, the conductive layer 21 has a function of the common electrodeof the liquid crystal element 20.

FIG. 13B illustrates an example in which an upper electrode in FIG. 8Cis used as the common electrode of the liquid crystal element 20. Forexample, the conductive layer 21 has both a function of the commonelectrode of the liquid crystal element 20 and a function of theelectrode of the touch sensor.

FIG. 14 illustrates an example in which an upper electrode in FIG. 11Cis used as the common electrode of the liquid crystal element 20. Forexample, the conductive layer 21 has both a function of the commonelectrode of the liquid crystal element 20 and a function of theelectrode of the touch sensor.

FIGS. 15A to 15C are each a schematic top view illustrating a touchpanel of one embodiment of the present invention. Therefore, mostcomponents other than those included in a touch sensor are notillustrated. Although not illustrated, a pixel electrode 51 has acomb-like top shape or a top shape provided with a slit in some cases.

In the structure illustrated in FIG. 15A, the touch sensor includes asensor electrode 55 and a sensor electrode 56. The sensor electrodes 55and 56 are formed using the same conductive film as the pixel electrode51. Alternatively, the sensor electrodes 55 and 56 are provided on thesame plane as the pixel electrode 51. A plurality of sensor electrodes55 arranged in the X direction are electrically connected to each otherthrough a wiring 57. The sensor electrode 56 extends in the Y direction.That is, FIG. 15A corresponds to a top view of FIG. 8A. The sensorelectrodes 55 and 56 may also be formed using not the same conductivefilm as the pixel electrode but the same conductive film as a commonelectrode.

FIG. 15B illustrates an example in which a common electrode 52 and thesensor electrode 55 are formed using the same conductive film.Alternatively, the common electrode 52 and the sensor electrode 55 areprovided on the same plane. The common electrode 52 and the sensorelectrode 55 each have a band-like shape that extends in the X directionand cross the sensor electrodes 56. That is, FIG. 15B corresponds to atop view of FIG. 8C.

FIG. 15C illustrates an example in which the common electrode 52 in FIG.15B also serves as the sensor electrode 55. That is, FIG. 15Ccorresponds to a top view of FIG. 7C.

In the above examples, the sensor electrode 56 extends in the Ydirection but may extend in the X direction. FIGS. 16A, 16B, and 16Ccorrespond to FIGS. 15A, 15B, and 15C, respectively, in which the sensorelectrode 56 extends in the X direction.

In the examples illustrated in FIGS. 15B and 15C, the upper electrode(the electrode close to the liquid crystal layer, that is, the electrodeclose to an object such as a finger or a stylus) serves as the pixelelectrode, and the lower electrode (the electrode apart from the liquidcrystal layer, that is, the electrode apart from an object such as afinger or a stylus) serves as the common electrode; however, oneembodiment of the present invention is not limited thereto. The upperelectrode (the electrode close to the liquid crystal layer, that is, theelectrode close to an object such as a finger or a stylus) can serve asthe common electrode, and the lower electrode (the electrode apart fromthe liquid crystal layer, that is, the electrode apart from an objectsuch as a finger or a stylus) can serve as the pixel electrode. FIGS.17A and 17B illustrate examples obtained by applying such a structure toFIGS. 15B and 15C, respectively. Although not illustrated, the commonelectrode 52 has a comb-like top shape or a top shape provided with aslit in some cases.

The above is the description of the touch panel.

Structure Example 1

More specific structure examples of the touch panel are described below.

FIG. 18A is a schematic perspective view of a touch panel 310 of oneembodiment of the present invention. FIG. 18B is a schematic perspectivedeveloped view of FIG. 18A. Note that only main components areillustrated for simplicity. In FIG. 18B, some components (such as asubstrate 372) are shown only in dashed outline.

The touch panel 310 includes a substrate 371 and the substrate 372 whichare provided so as to face each other.

A display portion 381, a driver circuit 382, a wiring 383, a drivercircuit 384, and the like are provided over the substrate 371. Aconductive layer 332 is formed in the display portion 381. The substrate371 is provided with an FPC 373 which is electrically connected to thewiring 383. In the example illustrated in FIGS. 18A and 18B, an IC 374is provided over the FPC 373.

A surface of the substrate 372 which faces the substrate 371 is providedwith a plurality of conductive layers 331, a plurality of conductivelayers 335, a plurality of conductive layers 341, and the like. Each ofthe conductive layers 341 is electrically connected to one of theplurality of conductive layers 331. The conductive layers 341 areelectrically connected to the FPC 373 provided over the substrate 371through a connection portion 385.

The conductive layer 335 is provided between the two conductive layers331. With the conductive layer 335, the generation of a differencebetween the transmittance of a region where the conductive layer 331 isprovided and the transmittance of a region where the conductive layer331 is not provided can be suppressed. The conductive layer 335 ispreferably electrically floating. With this structure, a change in thepotential of one of the conductive layers 331 and 332 can be efficientlytransmitted to the other through the conductive layer 335, therebyincreasing the detection sensitivity. The conductive layer 335 is notnecessarily provided, when it is not needed.

The display portion 381 includes at least a plurality of pixels. Each ofthe pixels includes at least one display element. It is preferable thateach of the pixels include a transistor and a display element. As thedisplay element, typically, a light-emitting element such as an organicEL element, a liquid crystal element, or the like can be used.

As the driver circuit 382, for example, a circuit functioning as a scanline driver circuit or a signal line driver circuit can be used.

The wiring 383 has a function of supplying a signal or electric power tothe display portion 381 or the driver circuit 382. The signal or theelectric power is input from the outside or the IC 374 to the wiring 383through the FPC 373.

The driver circuit 384 has a function of sequentially selecting theconductive layers 332. When the touch sensor is driven by sequentiallyselecting not the conductive layers 332 but the conductive layers 331,the driver circuit 384 has a function of switching a fixed potential anda sensing signal and supplying it to the conductive layers 332. In thecase where a signal for driving the touch sensor is supplied from the IC374 or the outside, the driver circuit 384 is not necessarily provided.

In the example illustrated in FIGS. 18A and 18B, the IC 374 is mountedon the FPC 373 by a chip-on-film (COF) method. As the IC 374, forexample, an IC functioning as a scan line driver circuit or a signalline driver circuit can be used. Note that it is possible that the IC374 is not provided when the touch panel 310 includes circuitsfunctioning as a scan line driver circuit and a signal line drivercircuit or when circuits functioning as a scan line driver circuit and asignal line driver circuit are provided outside and a signal for drivingthe display portion 381 is input through the FPC 373. The IC 374 mayalso be directly mounted on the substrate 371 by a chip-on-glass (COG)method or the like.

The touch sensor includes the conductive layer 331 provided over thesubstrate 372 and the conductive layer 332 provided over the substrate371. The touch sensor can perform detection by utilizing the capacitanceformed between the conductive layers 331 and 332.

With the above structure, the FPCs connected to the touch panel 310 canbe provided only on one substrate side (on the substrate 371 side inthis embodiment). Furthermore, it is preferable that the touch panel 310be provided with one FPC 373 which has a function of supplying signalsto both the display panel and the touch sensor as illustrated in FIGS.18A and 18B for the simplicity of the structure.

The IC 374 can have a function of driving the touch sensor.Alternatively, an IC for driving the touch sensor may further beprovided. Further alternatively, an IC for driving the touch sensor maybe mounted on the substrate 371.

FIG. 19 is a schematic top view of the touch panel 310 which has astructure different from that illustrated in FIGS. 18A and 18B.

The touch panel illustrated in FIG. 19 includes a plurality of FPCs 373a and an FPC 373 b over the substrate 371. Each of the FPCs 373 a has afunction of supplying a signal for driving the display portion 381. TheFPC 373 b has a function of supplying a signal or the like to theconductive layer 331 provided on the substrate 372 side.

The FPCs 373 a are provided along two or more sides of the displayportion 381 included in the touch panel 310 as described above; in thismanner, a lot of signals can be supplied to the touch panel 310. Forexample, in the case where the display portion 381 has a highresolution, by supplying signals to the display portion 381 from two ormore sides as described above, parasitic capacitance between wiringswhich is generated when the wirings are provided at high density can bereduced. In the case of a large display device, the above structure canshorten the length of the wirings and thus reduce wiring resistance andsuppress the influence of signal delay and the like.

Cross-Sectional Structure Example 1

Examples of the cross-sectional structure of a touch panel of oneembodiment of the present invention are described below with referenceto the drawings.

Cross-Sectional Structure Example 1-1

FIG. 20 is a schematic cross-sectional view of the touch panel 310. FIG.20 illustrates the cross sections of a region including the FPC 373, aregion including the driver circuit 382, and a region including thedisplay portion 381 in FIG. 18A.

The substrate 371 and the substrate 372 are attached to each other withan adhesive layer 151. A region surrounded by the substrate 371, thesubstrate 372, and the adhesive layer 151 is filled with liquid crystal253.

A transistor 201, a transistor 203, a connection portion 206, aconductive layer 207, a conductive layer 251 and a conductive layer 252included in a liquid crystal element 208, and the like are provided overthe substrate 371.

An insulating layer 211, an insulating layer 212, an insulating layer213, an insulating layer 214, an insulating layer 254, a spacer 216, andthe like are provided over the substrate 371. Part of the insulatinglayer 211 functions as a gate insulating layer of each transistor. Theinsulating layer 212, the insulating layer 213, and the insulating layer214 are provided to cover each transistor and the like. The insulatinglayer 214 functions as a planarization layer, for example. An example inwhich three insulating layers, the insulating layers 212, 213, and 214,are provided to cover the transistors and the like is described here;however, one embodiment of the present invention is not limited thereto,and four or more insulating layers, a single insulating layer, or twoinsulating layers may be provided. The insulating layer 214 functioningas a planarization layer is not necessarily provided when it is notneeded.

FIG. 20 illustrates the cross section of one sub-pixel as an example ofthe display portion 381. For example, the sub-pixel is a sub-pixelexhibiting a red color, a sub-pixel exhibiting a green color, or asub-pixel exhibiting a blue color; thus, full-color display can beachieved. The sub-pixel illustrated in FIG. 20 includes, for example,the transistor 203, the liquid crystal element 208, and a coloring layer231.

FIG. 20 illustrates, as an example of the driver circuit 382, an examplein which the transistor 201 is provided.

For example, in the example illustrated in FIG. 20 , the transistor 201has a structure in which a semiconductor layer where a channel is formedis provided between gate electrodes 283 and 284, and the transistor 203has a structure in which a semiconductor layer where a channel is formedis provided between gate electrodes 281 and 282. In the case where thegate electrodes 281 and 282 are connected to each other and the gateelectrodes 283 and 284 are connected to each other, such transistors canhave a higher field-effect mobility and thus have a higher on-statecurrent than other transistors. Consequently, a circuit capable ofhigh-speed operation can be obtained. Furthermore, the area occupied bya circuit portion can be reduced. The use of the transistor having ahigh on-state current can reduce signal delay in wirings and cansuppress display unevenness even in a display panel or a touch panel inwhich the number of wirings is increased because of increase in size orresolution.

Note that the transistor included in the driver circuit 382 and thetransistor included in the display portion 381 may have the samestructure. The plurality of transistors included in the driver circuit382 may have the same structure or different structures. The pluralityof transistors included in display portion 381 may have the samestructure or different structures.

For example, a material through which impurities such as water orhydrogen do not easily diffuse is preferably used for at least one ofthe insulating layers 212 and 213 which cover the transistors. That is,the insulating layer 212 or the insulating layer 213 can function as abarrier film. Such a structure can effectively suppress diffusion of theimpurities into the transistors from the outside, and a highly reliabletouch panel can be achieved.

In the example illustrated in FIG. 20 , a liquid crystal element using afringe field switching (FFS) mode is used as the liquid crystal element208. The liquid crystal element 208 includes the conductive layer 251,the liquid crystal 253, and the conductive layer 252. Orientation of theliquid crystal 253 can be controlled with an electric field generatedbetween the conductive layer 251 and the conductive layer 252.

The conductive layer 252 is provided over the insulating layer 214. Theinsulating layer 254 is provided so as to cover the conductive layer252, and the conductive layer 251 is provided over the insulating layer254. The conductive layer 251 is electrically connected to one of asource and a drain of the transistor 203 through an opening provided inthe insulating layers 254, 214, 213, and 212. With the conductive layers251 and 252 each formed using a light-transmitting conductive material,the touch panel 310 can be a transmissive liquid crystal display device.

The conductive layer 251 has a comb-like top shape or a top shapeprovided with a slit (a top shape is also referred to as a planarshape). The conductive layer 252 is provided so as to overlap with theconductive layer 251. In a region overlapping with the coloring layer231 and the like, there is a portion where the conductive layer 251 isnot provided over the conductive layer 252.

In FIG. 20 , the conductive layer 251 functions as a pixel electrode,and the conductive layer 252 functions as a common electrode.Alternatively, the conductive layer 251 which is provided in an upperlayer and has a comb-like top shape or a top shape provided with a slitmay be used as the common electrode, and the conductive layer 252 whichis provided in a lower layer may be used as the pixel electrode. In thatcase, the conductive layer 252 may be electrically connected to one ofthe source and the drain of the transistor 203.

The connection portion 206 is provided in a region near an end portionof the substrate 371. The connection portion 206 is electricallyconnected to the FPC 373 through a connection layer 209. In the exampleillustrated in FIG. 20 , the connection portion 206 is formed bystacking part of the conductive layer 207 and a conductive layer whichis formed by processing the same conductive film as the conductive layer251.

A surface of the substrate 372 which faces the substrate 371 is providedwith the conductive layer 331, the conductive layer 341, the coloringlayer 231, a light-blocking layer 232, an insulating layer 255, and thelike.

In FIG. 20 , the conductive layer 331 and the conductive layer 341 areformed on the same plane. The conductive layer 331 and the conductivelayer 341 are preferably formed by processing the same conductive filmat the same time. Alternatively, the conductive layer 331 and theconductive layer 341 may be continuous. In that case, at least a regionthat overlaps with the display portion 381 corresponds to the conductivelayer 331 functioning as one electrode of the touch sensor, and theother region corresponds to the conductive layer 341. That is, FIG. 20illustrates an example of a cross-sectional view in the case of FIG. 7A.

In the connection portion 385, the conductive layer 341 has a regionthat is not covered with the insulating layer 255. The conductive layer341 is electrically connected to the conductive layer 207 provided onthe substrate 371 side through a connector 386. Accordingly, the FPC 373is electrically connected to the conductive layer 331. In the exampleillustrated in FIG. 20 , a region where the connector 386 is in contactwith the conductive layer 341 and a region where the connector 386 is incontact with a conductive layer which is formed on the same plane as theconductive layer 251 and is electrically connected to the conductivelayer 207 are provided.

As the connector 386, a conductive particle can be used, for example. Asthe conductive particle, a particle of an organic resin, silica, or thelike coated with a metal material can be used. It is preferable to usenickel or gold as the metal material because contact resistance can bedecreased. It is also preferable to use a particle coated with layers oftwo or more kinds of metal materials, such as a particle coated withnickel and further with gold. As the connector 386, a material capableof elastic deformation or plastic deformation is preferably used. Asillustrated in FIG. 20 , the conductive particle has a shape that isvertically crushed in some cases. With the crushed shape, the contactarea between the connector 386 and a conductive layer electricallyconnected to the connector 386 can be increased, thereby reducingcontact resistance and suppressing the generation of problems such asdisconnection.

The connector 386 is preferably provided so as to be covered with theadhesive layer 151. For example, a paste or the like for forming theadhesive layer 151 may be applied, and then, the connector 386 may beprovided in the connection portion 385. A structure in which theconnection portion 385 is provided in a region provided with theadhesive layer 151 can be applied to, for example, a structure in whichthe adhesive layer 151 is provided in the peripheral region, e.g., adisplay device with a solid sealing structure, a display device with ahollow sealing structure, or the like.

The coloring layer 231 and the light-blocking layer 232 are provided onthe conductive layer 331. The insulating layer 255 is provided so as tocover the coloring layer 231 and the light-blocking layer 232.

The insulating layer 255 has a function of an overcoat preventingimpurities contained in the coloring layer 231, the light-blocking layer232, and the like from diffusing into the liquid crystal 253.

The spacer 216 is provided over the insulating layer 254 and has afunction of keeping a certain distance between the substrate 371 and thesubstrate 372. Although FIG. 20 illustrates the example in which thespacer 216 is in contact with components (e.g., the insulating layer255) on the substrate 372 side, the spacer 216 is not necessarily incontact with them. Moreover, FIG. 20 illustrates the example in whichthe spacer 216 is provided on the substrate 371 side; however, thespacer 216 may be provided on the substrate 372 side. For example, thespacer 216 can be provided between adjacent two sub-pixels. Aparticulate spacer may be used as the spacer 216. Although a materialsuch as silica can be used for the particulate spacer, an elasticmaterial such as an organic resin or rubber is preferably used. In thatcase, the particulate spacer may have a shape that is verticallycrushed.

Surfaces of the conductive layer 251, the insulating layer 254, theinsulating layer 255, and the like which are in contact with the liquidcrystal 253 may be provided with alignment films for controlling theorientation of the liquid crystal 253.

At least a region of the conductive layer 331 which overlaps with thecoloring layer 231 is preferably formed using a light-transmittingmaterial.

In the case of the liquid crystal element 208 that is a transmissiveliquid crystal element, for example, two polarizing plates which are notillustrated are provided such that the display portion is sandwichedtherebetween. Light from a backlight provided on the outer side of thepolarizing plate enters through the polarizing plate. At this time,orientation of the liquid crystal 253 is controlled with a voltageapplied between the conductive layer 251 and the conductive layer 252,whereby optical modulation of light can be controlled. In other words,the intensity of light emitted through the polarizing plate can becontrolled. Light entering from the backlight, excluding light in aparticular wavelength range, is absorbed by the coloring layer 231, sothat red, blue, or green light is emitted from the liquid crystalelement 208.

In addition to the polarizing plate, a circularly polarizing plate canbe used, for example. An example of the circularly polarizing plate is astack including a linear polarizing plate and a quarter-wave retardationplate. With the circularly polarizing plate, the viewing angledependency can be reduced.

In the example illustrated here, the liquid crystal element 20 is aliquid crystal element using an FFS mode. However, one embodiment of thepresent invention is not limited thereto, and a liquid crystal elementusing any of a variety of modes can be used. For example, a liquidcrystal element using a vertical alignment (VA) mode, a twisted nematic(TN) mode, an in-plane switching (IPS) mode, a fringe field switching(FFS) mode, an axially symmetric aligned micro-cell (ASM) mode, anoptically compensated birefringence (OCB) mode, a ferroelectric liquidcrystal (FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, orthe like can be used.

Furthermore, a normally black liquid crystal display device, forexample, a transmissive liquid crystal display device using a verticalalignment (VA) mode, may be used as the touch panel 310. Examples of thevertical alignment mode include a multi-domain vertical alignment (MVA)mode, a patterned vertical alignment (PVA) mode, and an advancedsuper-view (ASV) mode.

The liquid crystal element is an element that controls transmission andnon-transmission of light by optical modulation action of the liquidcrystal. Note that optical modulation action of the liquid crystal iscontrolled by an electric field applied to the liquid crystal (includinga horizontal electric field, a vertical electric field, and an obliqueelectric field). As the liquid crystal used for the liquid crystalelement, thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal (PDLC),ferroelectric liquid crystal, anti-ferroelectric liquid crystal, or thelike can be used. Such a liquid crystal material exhibits a cholestericphase, a smectic phase, a cubic phase, a chiral nematic phase, anisotropic phase, or the like depending on the conditions.

As the liquid crystal material, either of positive liquid crystal andnegative liquid crystal may be used, and an appropriate liquid crystalmaterial can be used depending on the mode or design to be used.

In the case of employing a horizontal electric field mode, liquidcrystal exhibiting a blue phase for which an alignment film isunnecessary may be used. A blue phase is one of liquid crystal phases,which is generated just before a cholesteric phase changes into anisotropic phase while the temperature of cholesteric liquid crystal isincreased. Since the blue phase appears only in a narrow temperaturerange, a liquid crystal composition in which several weight percent ormore of a chiral material is mixed is used for the liquid crystal layerin order to improve the temperature range. The liquid crystalcomposition which includes liquid crystal exhibiting a blue phase and achiral material has a short response time and has optical isotropy. Inaddition, the liquid crystal composition which includes liquid crystalexhibiting a blue phase and a chiral material does not need alignmenttreatment and has a small viewing angle dependence. An alignment filmdoes not need to be provided and rubbing treatment is thus notnecessary; accordingly, electrostatic discharge damage caused by therubbing treatment can be prevented, and defects and damage of the liquidcrystal display device in the manufacturing process can be reduced.

In this structure example, touch operation or the like can be detectedby utilizing the capacitance formed between the conductive layer 331 andthe conductive layer 252. That is, the conductive layer 252 serves asone of a pair of electrodes of the liquid crystal element 208 as well asone of a pair of electrodes of the touch sensor.

The conductive layer 251, 252, or 331 is preferably formed using aconductive material transmitting visible light. The conductive layer251, 252, or 331 is formed using, for example, a conductive materialcontaining a metal oxide. For example, a metal oxide amonglight-transmitting conductive materials described later can be used.

Alternatively, the conductive layer 251, 252, or 331 is preferablyformed using a metal oxide containing the same metal element as otherconductive layers or a semiconductor layer. In particular, in the casewhere an oxide semiconductor is used for the semiconductor layer of thetransistor in the touch panel 310, a conductive oxide containing a metalelement contained in the oxide semiconductor is preferably used. Theinsulating layer 254 may be formed using a silicon nitride filmcontaining hydrogen. In that case, the conductivity of the conductivelayer 252 which is formed using an oxide semiconductor can be improvedby hydrogen supplied from the insulating layer 254. That is, the oxidesemiconductor can be of an n⁺-type.

Depending on the conditions, a fixed potential may be supplied to theconductive layer 331. In that case, electromagnetic noise from theoutside can be blocked. For example, when sensing is not performed, aconstant potential that does not influence the switching of the liquidcrystal 253 may be supplied to the conductive layer 331. For example, aground potential, a common potential, or a predetermined constantpotential can be supplied. The conductive layer 331 and the conductivelayer 252 may be set at the same potential, for example.

By applying an appropriate potential to the conductive layer 331, acomponent in the thickness direction in the directions of an electricfield (the directions of the lines of electric force) generated betweenthe conductive layer 251 and the conductive layer 252 can be reduced,and an electric field can be effectively applied in the directionsubstantially perpendicular to the thickness direction (in the lateraldirection). Thus, an orientation defect in the liquid crystal 253 can besuppressed, and a malfunction such as light leakage can be prevented.

A substrate which an object such as a finger or a stylus directlytouches may be provided above the substrate 372. In that case, apolarizing plate or a circularly polarizing plate is preferably providedbetween the substrate 372 and the above substrate. In that case, theabove substrate is preferably provided with a protective layer (such asa ceramic coat). The protective layer can be formed using an inorganicinsulating material such as silicon oxide, aluminum oxide, yttriumoxide, or yttria-stabilized zirconia (YSZ). In addition, tempered glassmay be used for the above substrate. The tempered glass which can beused here is one that has been subjected to physical or chemicaltreatment by an ion exchange method, a thermal tempering method, or thelike and has a surface to which compressive stress has been applied.

[Components]

The above components are described below.

[Substrate]

A substrate having a flat surface can be used as the substrate includedin the touch panel. The substrate through which light emitted from thedisplay element is extracted is formed using a material that transmitsthe light. For example, a material such as glass, quartz, ceramics,sapphire, or an organic resin can be used. Alternatively, a singlecrystal semiconductor substrate or a polycrystalline semiconductorsubstrate made of silicon, silicon carbide, or the like, a compoundsemiconductor substrate made of silicon germanium or the like, an SOIsubstrate, or the like may be used. Still alternatively, any of thesesubstrates provided with a semiconductor element may be used as thesubstrate.

In the case where a glass substrate is used as the substrate, a largeglass substrate having any of the following sizes can be used: the 6thgeneration (1500 mm×1850 mm), the 7th generation (1870 mm×2200 mm), the8th generation (2200 mm×2400 mm), the 9th generation (2400 mm×2800 mm),and the 10th generation (2950 mm×3400 mm). Thus, a large-sized displaydevice can be manufactured. Alternatively, a flexible substrate may beused as the substrate, and a transistor, a capacitor, or the like may beprovided directly over the flexible substrate.

The weight and thickness of the touch panel can be decreased by using athin substrate. Furthermore, a flexible touch panel can be obtained byusing a substrate that is thin enough to have flexibility.

As the glass, for example, non-alkali glass, barium borosilicate glass,aluminoborosilicate glass, or the like can be used.

Examples of a material having flexibility and a light-transmittingproperty with respect to visible light include glass that is thin enoughto have flexibility, polyester resins such as polyethylene terephthalate(PET) and polyethylene naphthalate (PEN), a polyacrylonitrile resin, apolyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC)resin, a polyethersulfone (PES) resin, a polyamide resin, a cycloolefinresin, a polystyrene resin, a polyamide imide resin, a polyvinylchloride resin, and a polytetrafluoroethylene (PTFE) resin. Inparticular, a material whose thermal expansion coefficient is low ispreferred, and for example, a polyamide imide resin, a polyimide resin,or PET can be suitably used. A substrate in which a glass fiber isimpregnated with an organic resin or a substrate whose thermal expansioncoefficient is reduced by mixing an organic resin with an inorganicfiller can also be used. A substrate using such a material islightweight, and thus, a touch panel using this substrate can also belightweight.

Since the substrate through which light is not extracted does not needto have a light-transmitting property, a metal substrate using a metalmaterial or an alloy material, a ceramic substrate, a semiconductorsubstrate, or the like can be used as well as the above-describedsubstrates. A metal material and an alloy material, which have highthermal conductivity, are preferable because they can easily conductheat to the whole sealing substrate and accordingly can prevent a localtemperature rise in the touch panel. To obtain flexibility andbendability, the thickness of a metal substrate is preferably greaterthan or equal to 10 μm and less than or equal to 200 μm, more preferablygreater than or equal to 20 μm and less than or equal to 50 μm.

There is no particular limitation on a material of the metal substrate,but it is preferable to use, for example, aluminum, copper, nickel, or ametal alloy such as an aluminum alloy or stainless steel.

It is preferable to use a substrate subjected to insulation treatment insuch a manner that a surface of a conductive substrate is oxidized or aninsulating film is formed on a surface. An insulating film may be formedby, for example, a coating method such as a spin-coating method or adipping method, an electrodeposition method, an evaporation method, or asputtering method. An oxide film may be formed on the substrate surfaceby an anodic oxidation method, exposing to or heating in an oxygenatmosphere, or the like.

The flexible substrate may have a stacked structure of a layer of any ofthe above-mentioned materials and a hard coat layer (e.g., a siliconnitride layer) which protects a surface of the touch panel from damageor the like, a layer (e.g., an aramid resin layer) which can dispersepressure, or the like. Furthermore, to suppress a decrease in thelifetime of the display element due to moisture and the like, aninsulating film with low water permeability may be provided. Forexample, a film containing nitrogen and silicon (e.g., a silicon nitridefilm or a silicon oxynitride film) or a film containing nitrogen andaluminum (e.g., an aluminum nitride film) may be provided.

The substrate may be formed by stacking a plurality of layers. Inparticular, when a glass layer is used, a barrier property against waterand oxygen can be improved, and thus, a highly reliable touch panel canbe provided.

A substrate in which a glass layer, an adhesive layer, and an organicresin layer are stacked from the side closer to the display element canbe used, for example. The thickness of the glass layer is greater thanor equal to 20 μm and less than or equal to 200 μm, preferably greaterthan or equal to 25 μm and less than or equal to 100 μm. With such athickness, the glass layer can have both a high barrier property againstwater and oxygen and a high flexibility. The thickness of the organicresin layer is greater than or equal to 10 μm and less than or equal to200 μm, preferably greater than or equal to 20 μm and less than or equalto 50 μm. By providing such an organic resin layer, occurrence of abreak or a crack in the glass layer can be inhibited, and the mechanicalstrength can be improved. With the substrate that includes such acomposite material of a glass material and an organic resin, a highlyreliable flexible touch panel can be provided.

[Transistor]

The transistor includes a conductive layer functioning as the gateelectrode, the semiconductor layer, a conductive layer functioning asthe source electrode, a conductive layer functioning as the drainelectrode, and the insulating layer functioning as the gate insulatinglayer. In the above example, a bottom-gate transistor is used.

Note that there is no particular limitation on the structure of thetransistor included in the touch panel of one embodiment of the presentinvention. For example, a planar transistor, a staggered transistor, oran inverted staggered transistor may be used. A top-gate transistor or abottom-gate transistor may be used. Gate electrodes may be providedabove and below a channel. There is no particular limitation on asemiconductor material used for the transistor, and an oxidesemiconductor, silicon, or germanium can be used, for example.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistor, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle-crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. It is preferable that a semiconductorhaving crystallinity be used, in which case deterioration of thetransistor characteristics can be suppressed.

As a semiconductor material for the semiconductor layer of thetransistor, an element of Group 14, a compound semiconductor, or anoxide semiconductor can be used, for example. Typically, a semiconductorcontaining silicon, a semiconductor containing gallium arsenide, anoxide semiconductor containing indium, or the like can be used.

An oxide semiconductor is preferably used as a semiconductor in which achannel of the transistor is formed. In particular, an oxidesemiconductor having a wider band gap than silicon is preferably used. Asemiconductor material having a wider band gap and a lower carrierdensity than silicon is preferably used because the off-state current ofthe transistor can be reduced.

For example, the oxide semiconductor preferably contains at least indium(In) or zinc (Zn). The oxide semiconductor more preferably includes anIn-M-Zn oxide (M is a metal such as Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce,Hf, or Nd).

As the semiconductor layer, it is particularly preferable to use anoxide semiconductor film including a plurality of crystal parts whosec-axes are aligned substantially perpendicular to a surface on which thesemiconductor layer is formed or the top surface of the semiconductorlayer and in which a grain boundary is not observed between adjacentcrystal parts.

There is no grain boundary in such an oxide semiconductor; therefore,generation of a crack in an oxide semiconductor film which is caused bystress when a display panel is bent is prevented. Therefore, such anoxide semiconductor can be preferably used for a flexible touch panelwhich is used in a bent state, or the like.

Moreover, the use of such an oxide semiconductor with crystallinity forthe semiconductor layer makes it possible to provide a highly reliabletransistor in which a variation in electrical characteristics issuppressed.

A transistor with an oxide semiconductor whose band gap is wider thanthat of silicon can hold electric charge stored in a capacitor that isseries-connected to the transistor for a long time, owing to a lowoff-state current of the transistor. When such a transistor is used fora pixel, operation of a driver circuit can be stopped while a gray scaleof an image displayed in each display region is maintained. As a result,a display device with an extremely low power consumption can beobtained.

The semiconductor layer preferably includes a film represented by anIn-M-Zn oxide that contains, for example, at least indium (In), zinc(Zn), and M (a metal such as Al, Ti, Ga, Y, Zr, La, Ce, Sn, or Hf). Inorder to reduce variations in electrical characteristics of thetransistor including the oxide semiconductor, the oxide semiconductorpreferably contains a stabilizer in addition to the above elements.

Examples of the stabilizer, including metals that can be used as M, aregallium (Ga), tin (Sn), hafnium (Hf), aluminum (Al), and zirconium (Zr).Other examples of the stabilizer are lanthanoid such as lanthanum (La),cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium(Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho),erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

As an oxide semiconductor included in the semiconductor layer, any ofthe following oxides can be used, for example: an In—Ga—Zn-based oxide,an In—Al—Zn-based oxide, an In—Sn—Zn-based oxide, an In—Hf—Zn-basedoxide, an In—La—Zn-based oxide, an In—Ce—Zn-based oxide, anIn—Pr—Zn-based oxide, an In—Nd—Zn-based oxide, an In—Sm—Zn-based oxide,an In—Eu—Zn-based oxide, an In—Gd—Zn-based oxide, an In—Tb—Zn-basedoxide, an In—Dy—Zn-based oxide, an In—Ho—Zn-based oxide, anIn—Er—Zn-based oxide, an In—Tm—Zn-based oxide, an In—Yb—Zn-based oxide,an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-based oxide, anIn—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, anIn—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, and anIn—Hf—Al—Zn-based oxide.

Note that here, an “In—Ga—Zn-based oxide” means an oxide containing In,Ga, and Zn as its main components, and there is no limitation on theratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain another metalelement in addition to In, Ga, and Zn.

The semiconductor layer and the conductive layer may include the samemetal elements contained in the above oxides. The use of the same metalelements for the semiconductor layer and the conductive layer can reducethe manufacturing cost. For example, when metal oxide targets with thesame metal composition are used, the manufacturing cost can be reduced,and the same etching gas or the same etchant can be used in processingthe semiconductor layer and the conductive layer. Note that even whenthe semiconductor layer and the conductive layer include the same metalelements, they have different compositions in some cases. For example, ametal element in a film is released during the manufacturing process ofthe transistor and the capacitor, which might result in different metalcompositions.

Note that in the case where the semiconductor layer includes an In-M-Znoxide, when the summation of In and M is assumed to be 100 atomic %, theatomic proportions of In and M, not taking Zn and O into consideration,are preferably higher than 25 atomic % and lower than 75 atomic %,respectively, more preferably higher than 34 atomic % and lower than 66atomic %, respectively.

The energy gap of the semiconductor layer is 2 eV or more, preferably2.5 eV or more, more preferably 3 eV or more. In this manner, theoff-state current of the transistor can be reduced by using an oxidesemiconductor having a wide energy gap.

The thickness of the semiconductor layer is greater than or equal to 3nm and less than or equal to 200 nm, preferably greater than or equal to3 nm and less than or equal to 100 nm, more preferably greater than orequal to 3 nm and less than or equal to 50 nm.

In the case where the semiconductor layer includes an In-M-Zn oxide (Mrepresents Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce, Hf, or Nd), it ispreferable that the atomic ratio of metal elements of a sputteringtarget used for forming a film of the In-M-Zn oxide satisfy In M and ZnM. As the atomic ratio of the metal elements of such a sputteringtarget, In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, and In:M:Zn=4:2:3are preferable. Note that the atomic ratio of metal elements in theformed semiconductor layer varies from the above atomic ratio of metalelements of the sputtering target within a range of ±40% as an error.

An oxide semiconductor film with a low carrier density is used as thesemiconductor layer. For example, an oxide semiconductor film whosecarrier density is lower than or equal to 1×10¹⁷/cm³, preferably lowerthan or equal to 1×10¹⁵/cm³, more preferably lower than or equal to1×10¹³/cm³, more preferably lower than or equal to 1×10¹¹/cm³ is used asthe semiconductor layer.

Note that, without limitation to the compositions and materialsdescribed above, a material with an appropriate composition may be useddepending on required semiconductor characteristics and electricalcharacteristics (e.g., field-effect mobility and threshold voltage) ofthe transistor. Furthermore, to obtain required semiconductorcharacteristics of the transistor, it is preferable that the carrierdensity, the impurity concentration, the defect density, the atomicratio of a metal element to oxygen, the interatomic distance, thedensity, and the like of the semiconductor layer be set to beappropriate.

When silicon or carbon which is one of elements belonging to Group 14 iscontained in the semiconductor layer, oxygen vacancies are increased,and the semiconductor layer has n-type conductivity. Thus, theconcentration of silicon or carbon (measured by secondary ion massspectrometry (SIMS)) of the semiconductor layer is lower than or equalto 2×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁷ atoms/cm³.

Furthermore, the concentration of alkali metal or alkaline earth metalin the semiconductor layer, which is measured by SIMS, is lower than orequal to 1×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁶atoms/cm³. Alkali metal and alkaline earth metal might generate carrierswhen bonded to an oxide semiconductor, in which case the off-statecurrent of the transistor might be increased. Therefore, it ispreferable to reduce the concentration of alkali metal or alkaline earthmetal in the semiconductor layer.

When nitrogen is contained in the semiconductor layer, electrons servingas carriers are generated to increase the carrier density, so that thesemiconductor layer easily has n-type conductivity. Thus, a transistorincluding an oxide semiconductor which contains nitrogen is likely to benormally on. For this reason, nitrogen in the oxide semiconductor filmis preferably reduced as much as possible; the concentration of nitrogenwhich is measured by SIMS is preferably set to, for example, lower thanor equal to 5×10¹⁸ atoms/cm³.

The semiconductor layer may have a non-single-crystal structure, forexample. The non-single-crystal structure includes a c-axis alignedcrystalline oxide semiconductor (CAAC-OS) which is described later, apolycrystalline structure, a microcrystalline structure which isdescribed later, or an amorphous structure, for example. Among thenon-single-crystal structures, an amorphous structure has the highestdensity of defect states, whereas CAAC-OS has the lowest density ofdefect states.

The semiconductor layer may have an amorphous structure, for example. Anoxide semiconductor film having an amorphous structure has disorderedatomic arrangement and no crystalline component, for example.Alternatively, an oxide film having an amorphous structure has, forexample, an absolutely amorphous structure and no crystal part.

Note that the semiconductor layer may be a mixed film including two ormore of the following: a region having an amorphous structure, a regionhaving a microcrystalline structure, a region having a polycrystallinestructure, a region of CAAC-OS, and a region having a single-crystalstructure. Furthermore, the mixed film has a stacked-layer structure oftwo or more of the following in some cases: the region having anamorphous structure, the region having a microcrystalline structure, theregion having a polycrystalline structure, the region of CAAC-OS, andthe region having a single-crystal structure.

Alternatively, silicon is preferably used as a semiconductor in which achannel of the transistor is formed. Although amorphous silicon may beused as silicon, silicon having crystallinity is particularlypreferable. For example, microcrystalline silicon, polycrystallinesilicon, single crystal silicon, or the like is preferably used. Inparticular, polycrystalline silicon can be formed at a lower temperaturethan single crystal silicon and has a higher field-effect mobility and ahigher reliability than amorphous silicon. When such a polycrystallinesemiconductor is used for a pixel, the aperture ratio of the pixel canbe improved. Even in the case where pixels are provided at extremelyhigh resolution, a gate driver circuit and a source driver circuit canbe formed over a substrate over which the pixels are formed, and thenumber of components of an electronic device can be reduced.

[Conductive Layer]

As conductive layers such as a gate, a source, and a drain of thetransistor and a wiring and an electrode in the touch panel, asingle-layer structure or a stacked-layer structure using any of metalssuch as aluminum, titanium, chromium, nickel, copper, yttrium,zirconium, molybdenum, silver, tantalum, and tungsten, or an alloycontaining any of these metals as its main component can be used. Forexample, a single-layer structure of an aluminum film containingsilicon, a two-layer structure in which an aluminum film is stacked overa titanium film, a two-layer structure in which an aluminum film isstacked over a tungsten film, a two-layer structure in which a copperfilm is stacked over a copper-magnesium-aluminum alloy film, a two-layerstructure in which a copper film is stacked over a titanium film, atwo-layer structure in which a copper film is stacked over a tungstenfilm, a three-layer structure in which a titanium film or a titaniumnitride film, an aluminum film or a copper film, and a titanium film ora titanium nitride film are stacked in this order, a three-layerstructure in which a molybdenum film or a molybdenum nitride film, analuminum film or a copper film, and a molybdenum film or a molybdenumnitride film are stacked in this order, and the like can be given. Notethat a transparent conductive material containing indium oxide, tinoxide, or zinc oxide may also be used. Copper containing manganese ispreferably used because controllability of a shape by etching isincreased.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zincoxide to which gallium is added, or graphene can be used. Alternatively,a metal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium, or an alloy material containing any of these metal materialscan be used. Alternatively, a nitride of the metal material (e.g.,titanium nitride) or the like may be used. In the case of using themetal material or the alloy material (or the nitride thereof), thethickness is set small enough to be able to transmit light.Alternatively, a stack of any of the above materials can be used as theconductive layer. For example, a stacked film of indium tin oxide and analloy of silver and magnesium is preferably used because theconductivity can be increased.

Alternatively, for the conductive layer, an oxide semiconductor similarto that of the semiconductor layer is preferably used. In that case, itis preferable that the conductive layer be formed to have a lowerelectric resistance than a region in the semiconductor layer where achannel is formed.

For example, such a conductive layer can be used as the conductive layerfunctioning as the second gate electrode of the transistor.Alternatively, it can be used as another light-transmitting conductivelayer.

[Method for Controlling Resistivity of Oxide Semiconductor]

An oxide semiconductor film that can be used as each of thesemiconductor layer and the conductive layer includes a semiconductormaterial whose resistivity can be controlled by oxygen vacancies in thefilm and/or the concentration of impurities such as hydrogen or water inthe film. Thus, treatment to be performed on the semiconductor layer andthe conductive layer is selected from the following to control theresistivity of each of the oxide semiconductor films: treatment forincreasing oxygen vacancies and/or the impurity concentration andtreatment for reducing oxygen vacancies and/or the impurityconcentration.

Specifically, plasma treatment is performed on the oxide semiconductorfilm used as the conductive layer to increase oxygen vacancies and/orimpurities such as hydrogen or water in the oxide semiconductor film, sothat the oxide semiconductor film can have a high carrier density and alow resistivity. Furthermore, an insulating film containing hydrogen isformed in contact with the oxide semiconductor film to diffuse hydrogenfrom the insulating film containing hydrogen to the oxide semiconductorfilm, so that the oxide semiconductor film can have a high carrierdensity and a low resistivity.

The semiconductor layer that functions as the channel region of thetransistor is not in contact with the insulating films containinghydrogen. With the use of an insulating film containing oxygen, in otherwords, an insulating film capable of releasing oxygen, for at least oneof the insulating films in contact with the semiconductor layer, oxygencan be supplied to the semiconductor layer. The semiconductor layer towhich oxygen is supplied is an oxide semiconductor film having a highresistivity because oxygen vacancies in the film or at the interface arecompensated. Note that as the insulating film capable of releasingoxygen, a silicon oxide film or a silicon oxynitride film can be used,for example.

To reduce the resistivity of the oxide semiconductor film, an ionimplantation method, an ion doping method, a plasma immersion ionimplantation method, or the like can be employed to inject hydrogen,boron, phosphorus, or nitrogen into the oxide semiconductor film.

To reduce the resistivity of the oxide semiconductor film, plasmatreatment may be performed on the oxide semiconductor film. For theplasma treatment, for example, a gas containing at least one of a raregas (He, Ne, Ar, Kr, or Xe), hydrogen, and nitrogen is typically used.Specifically, plasma treatment in an Ar atmosphere, plasma treatment ina mixed gas atmosphere of Ar and hydrogen, plasma treatment in anammonia atmosphere, plasma treatment in a mixed gas atmosphere of Ar andammonia, plasma treatment in a nitrogen atmosphere, or the like can beemployed.

In the oxide semiconductor film subjected to the plasma treatment, anoxygen vacancy is formed in a lattice from which oxygen is released (orin a portion from which oxygen is released). This oxygen vacancy cangenerate a carrier. When hydrogen is supplied from an insulating filmthat is in the vicinity of the oxide semiconductor film, specifically,that is in contact with the lower surface or the upper surface of theoxide semiconductor film, and hydrogen is bonded to the oxygen vacancy,an electron serving as a carrier might be generated.

The oxide semiconductor film in which oxygen vacancies are filled withoxygen and the hydrogen concentration is reduced can be referred to as ahighly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film. The term “substantially intrinsic” refers tothe state where the oxide semiconductor film has a carrier density oflower than 8×10¹¹/cm³, preferably lower than 1×10¹¹/cm³, more preferablylower than 1×10¹⁰/cm³. A highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor film has few carriergeneration sources and thus can have a low carrier density. The highlypurified intrinsic or substantially highly purified intrinsic oxidesemiconductor film has a low density of defect states and accordinglycan have a low density of trap states.

The highly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film has an extremely low off-state current; evenwhen an element has a channel width of 1×10⁶ μm and a channel length of10 μm, the off-state current can be lower than or equal to themeasurement limit of a semiconductor parameter analyzer, i.e., lowerthan or equal to 1×10⁻¹³ A, at a voltage (drain voltage) between asource electrode and a drain electrode of from 1 V to 10 V. Accordingly,the transistor in which the channel region is formed in thesemiconductor layer that is a highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor film can have a smallvariation in electrical characteristics and a high reliability.

For example, an insulating film containing hydrogen, in other words, aninsulating film capable of releasing hydrogen, typically, a siliconnitride film, is used as the insulating film in contact with the oxidesemiconductor film used as the conductive layer, whereby hydrogen can besupplied to the conductive layer. The hydrogen concentration in theinsulating film capable of releasing hydrogen is preferably higher thanor equal to 1×10²² atoms/cm³. Such an insulating film is formed incontact with the conductive layer, whereby hydrogen can be effectivelycontained in the conductive layer. In this manner, the resistivity ofthe oxide semiconductor film can be controlled by changing thestructures of the insulating films in contact with the semiconductorlayer and the conductive layer.

Hydrogen contained in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water and also causes an oxygen vacancy ina lattice from which oxygen is released (or a portion from which oxygenis released). Due to entry of hydrogen into the oxygen vacancy, anelectron serving as a carrier is generated in some cases. Furthermore,in some cases, bonding of part of hydrogen to oxygen bonded to a metalatom causes generation of an electron serving as a carrier. Accordingly,the conductive layer formed in contact with the insulating filmcontaining hydrogen is an oxide semiconductor film that has a highercarrier density than the semiconductor layer.

Hydrogen in the semiconductor layer of the transistor in which a channelregion is formed is preferably reduced as much as possible.Specifically, in the semiconductor layer, the concentration of hydrogenwhich is measured by SIMS is lower than or equal to 2×10²⁰ atoms/cm³,preferably lower than or equal to 5×10¹⁹ atoms/cm³, more preferablylower than or equal to 1×10¹⁹ atoms/cm³, more preferably lower than5×10¹⁸ atoms/cm³, more preferably lower than or equal to 1×10¹⁸atoms/cm³, more preferably lower than or equal to 5×10¹⁷ atoms/cm³, morepreferably lower than or equal to 1×10¹⁶ atoms/cm³.

The conductive layer is an oxide semiconductor film that has a higherhydrogen concentration and/or a larger number of oxygen vacancies (i.e.,a lower resistivity) than the semiconductor layer. The hydrogenconcentration in the conductive layer is higher than or equal to 8×10¹⁹atoms/cm³, preferably higher than or equal to 1×10²⁰ atoms/cm³, morepreferably higher than or equal to 5×10²⁰ atoms/cm³. The hydrogenconcentration in the conductive layer is greater than or equal to 2times, preferably greater than or equal to 10 times the hydrogenconcentration in the semiconductor layer. The resistivity of theconductive layer is preferably greater than or equal to 1×10⁻⁸ times andless than 1×10⁻¹ times the resistivity of the semiconductor layer. Theresistivity of the conductive layer is typically higher than or equal to1×10⁻³ Ωcm and lower than 1×10⁴ Ωcm, preferably higher than or equal to1×10⁻³ Ωcm and lower than 1×10⁻¹ Ωcm.

[Insulating Layer]

Examples of an insulating material that can be used for the insulatinglayers, the overcoat, the spacer, and the like include a resin such asan acrylic or an epoxy, a resin having a siloxane bond, and an inorganicinsulating material such as silicon oxide, silicon oxynitride, siliconnitride oxide, silicon nitride, or aluminum oxide.

[Adhesive Layer]

For the adhesive layer, a curable resin such as a heat curable resin, aphotocurable resin, or a two-component type curable resin can be used.For example, an acrylic resin, a urethane resin, an epoxy resin, or aresin having a siloxane bond such as silicone can be used.

[Connection Layer]

For the connection layer, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

[Coloring Layer]

Examples of a material that can be used for the coloring layer include ametal material, a resin material, and a resin material containing apigment or dye.

The above is the description of the components.

Cross-Sectional Structure Example 1-2

FIG. 21 illustrates a cross-sectional structure example of a touch panelwhich partly differs from the above example. Note that the descriptionof the portions already described is omitted and different portions aredescribed.

FIG. 21 illustrates an example in which the coloring layer 231 isprovided on the substrate 371 side. Specifically, the coloring layer 231is provided in contact with the upper surface of the insulating layer213. The insulating layer 214 functioning as a planarization layer isprovided so as to cover the coloring layer 231.

With such a structure, the structure of the substrate 372 can be moresimplified. For example, in FIG. 21 , the substrate 372 is provided withonly the conductive layers 331 and 341. Note that the substrate 372 mayalso be provided with an alignment film or the like when it is needed.

Cross-Sectional Structure Example 1-3

FIG. 22 illustrates an example in which the transistors 201 and 203 inFIG. 20 each have a top-gate structure.

Each of the transistors includes a semiconductor layer, and a gateelectrode is provided over the semiconductor layer with the insulatinglayer 211 provided therebetween. The semiconductor layer may include alow-resistance region. The low-resistance region functions as a sourceor a drain.

The source electrodes and the drain electrodes of the transistors areprovided over the insulating layer 213 and electrically connected to thelow-resistance regions in the semiconductor layers through openingsprovided in the insulating layers 213, 212, and 211.

The low-resistance region in the semiconductor layer can be, forexample, a region containing more impurities than a region where achannel of the transistor is formed, a region with a high carrierconcentration, a region with low crystallinity, or the like. An impuritywhich can increase the conductivity depends on a semiconductor used forthe semiconductor layer; typically, an element that can impart n-typeconductivity, such as phosphorus, an element that can impart p-typeconductivity, such as boron, a rare gas such as helium, neon, or argon,hydrogen, lithium, sodium, magnesium, aluminum, nitrogen, fluorine,potassium, calcium, or the like can be given. In addition to the aboveelements, titanium, iron, nickel, copper, zinc, silver, indium, tin, orthe like also functions as an impurity which influences the conductivityof the semiconductor. For example, a region 262 and a region 263 containthe above impurity at a higher concentration than the region where achannel of the transistor is formed.

Cross-Sectional Structure Example 1-4

FIG. 23 illustrates an example in which the positon of the conductivelayer 252 is different from those in FIG. 20 and the like. Specifically,the conductive layer 252 is provided between the insulating layer 212and the insulating layer 213.

For the conductive layer 252, for example, any of the above-describedlight-transmitting conductive materials can be used.

In addition, for example, the conductive layer 252 preferably includes alow-resistance oxide semiconductor. In particular, in the case where anoxide semiconductor is used for the semiconductor layer of thetransistor in the touch panel 310, the conductive layer 252 ispreferably formed using an oxide semiconductor whose resistivity islower than that of the oxide semiconductor used for the semiconductorlayer.

The resistivity of the conductive layer 252 can be reduced, for example,by the method for controlling the resistivity of an oxide semiconductorwhich is described above.

In that case, the insulating layer containing much hydrogen ispreferably used as the insulating layer 213 covering the conductivelayer 252. In particular, the insulating layer 213 preferably includesan insulating film containing silicon nitride.

Cross-Sectional Structure Example 2

Cross-sectional structure examples of the touch panel partly differentfrom the above cross-sectional structure examples are described below.

Cross-Sectional Structure Example 2-1

A cross-sectional structure example in FIG. 24 is different from theabove cross-sectional structure examples in that the conductive layer331 and the conductive layer 341 are provided on the substrate 371 side.

The conductive layers 331 and 341 are provided over the substrate 371.The insulating layer 217 is provided so as to cover the conductivelayers 331 and 341. The transistor 201, the transistor 203, and the likeare provided over the insulating layer 217.

In the connection portion 385, the conductive layer 341 is electricallyconnected to the conductive layer 207 through an opening in theinsulating layer 217.

Touch operation can be detected by utilizing the capacitance generatedbetween the conductive layers 331 and 252.

With such a structure, the structure of the substrate 372 can besimplified.

For the conductive layers 331 and 341, a conductive material with highheat resistance is preferably used. In the case where a light-blockingmaterial such as a metal is used for the conductive layer 331, anopening is preferably provided in a region overlapping with the coloringlayer 231 as illustrated in FIG. 24 .

The conductive layer 331 is preferably provided in a position that doesnot overlap with the transistor 203 and the like as illustrated in FIG.24 . Alternatively, an opening is preferably provided in the conductivelayer 331 in a region overlapping with the transistor 203 and the like.With such a structure, a malfunction of the transistor 203 and the likedue to a change in potential of the conductive layer 331 can besuppressed.

Cross-Sectional Structure Example 2-2

FIG. 25 illustrates an example in which, as in FIG. 21 , the coloringlayer 231 is provided on the substrate 371 side in the structureillustrated in FIG. 24 .

Providing the conductive layer 331, the conductive layer 341, and thecoloring layer 231 on the substrate 371 side as described above enablesa structure in which the substrate 372 is provided with no component.Alignment films may be provided on regions of the substrates 371 and 372which are in contact with the liquid crystal layer.

Structure Example 2

Structure examples of the touch panel partly different from thestructure example 1 are described below with reference to the drawings.

In a touch panel of one embodiment of the present invention which willbe described below, at least one of a pair of conductive layers includedin a touch sensor is formed of the same conductive film as at least oneof a pair of conductive layers included in a liquid crystal element. Atleast one of the pair of conductive layers included in the touch sensorand at least one of the pair of conductive layers included in the liquidcrystal element are provided on the same plane. Alternatively, at leastone of the pair of conductive layers included in the touch sensor isprovided so as to also serve as at least one of the pair of conductivelayers included in the liquid crystal element. That is, one conductivefilm has both a function of at least one of the pair of conductivelayers included in the touch sensor and a function of at least one ofthe pair of conductive layers included in the liquid crystal element.With such a structure, the manufacturing process of the touch panel canbe simplified, thereby more reducing the manufacturing cost.

Structure Example 2-1

FIG. 26 is a schematic top view illustrating an example of the layout ofa pair of conductive layers functioning as electrodes of a liquidcrystal element and a pair of conductive layers included in a touchsensor. As an example, a liquid crystal element using an FFS mode isdescribed.

FIG. 27 is a schematic cross-sectional view of the touch panel,including the cross section along the section line X1-X2 in FIG. 26 .FIG. 26 and FIG. 27 correspond to FIG. 8A.

Conductive layers 401 each have an island shape and are arranged in theX direction and the Y direction in a matrix. Each of the conductivelayers 401 includes a slit. A conductive layer 402 is provided so as tooverlap with the conductive layers 401. Here, the conductive layer 401functions as the pixel electrode, and the conductive layer 402 functionsas the common electrode. The case where the conductive layer 401 on theupper side is a pixel electrode and the conductive layer 402 on thelower side is a common electrode is described in this example; however,the functions of these conductive layers may be reversed.

A conductive layer 411 a and a conductive layer 411 b extending in the Ydirection are each provided so as to be located between the adjacent twoconductive layers 401.

A conductive layer 412 a extending in the X direction includes aconductive layer 404 and a conductive layer 405. The conductive layer404 has a band-like shape whose longitudinal direction is parallel tothe X direction and is provided, for example, between the conductivelayers 411 a and 411 b. The conductive layer 405 includes a regionoverlapping with the conductive layer 411 a or 411 b and electricallyconnects the two conductive layers 404, which sandwich the conductivelayer 411 a or 411 b, through a contact hole. The conductive layer 405overlaps with the conductive layer 411 a or 411 b with an insulatinglayer that is not illustrated provided therebetween. Alternatively, theconductive layer 405 may extend in the X direction as illustrated inFIG. 28 . In this manner, the wiring resistance of the conductive layer404 can be substantially reduced.

Alternatively, in FIG. 26 or FIG. 28 , the conductive layers 411 a and411 b may extend in the X direction, and the conductive layers 412 a and412 b may extend in the Y direction.

The conductive layers 411 a, 411 b, 404, and 401 are formed byprocessing the same conductive film. Therefore, the conductive layers411 a, 411 b, 404, and 401 are provided on the same plane.

In this example, the conductive layer 405 is formed by processing thesame conductive film as source and drain electrodes 285 of thetransistor. In that case, the layout of the conductive layer 405 has noproblem even when a gate electrode and the like are provided below theconductive layer 405. Thus, the conductive layer 405 can be provided soas to overlap with the gate electrode or a film formed by processing thesame conductive film as the gate electrode. However, one embodiment ofthe present invention is not limited thereto, and the conductive layer405 can be formed by processing the same conductive film as the gateelectrode 281, the semiconductor layer, or other conductive layers ofthe transistor.

FIG. 29 illustrates, as an example, the case where the conductive layer405 is formed by processing the same conductive film as the gateelectrode. In that case, the layout of the conductive layer 405 has noproblem even when the source and drain electrodes 285 and the like areprovided over the conductive layer 405. Thus, the conductive layer 405can be provided so as to overlap with or to cross the source and drainelectrodes 285 or a film formed by processing the same conductive filmas the source and drain electrodes 285. That is, a source signal line (awiring having a function of supplying a video signal to each pixel) canbe provided so as to overlap with the conductive layer 411 a or 411 b.Thus, the layout area of the conductive layer 401 can be large. That is,the aperture ratio can be increased.

FIG. 30 illustrates the case where the conductive layer 405 is formed byprocessing the same conductive film as the conductive layer 402. In thatcase, the layout of the conductive layer 405 has no problem even whenthe source and drain electrodes 285, the gate electrode, and the likeare provided below the conductive layer 405. Thus, the conductive layer405 can be provided so as to overlap with or to cross the gate electrodeor the source and drain electrodes 285, a film formed by processing thesame conductive film as the gate electrode, or a film formed byprocessing the same conductive film as the source and drain electrodes285. That is, the source signal line (a wiring having a function ofsupplying a video signal to each pixel) can be provided so as to overlapwith the conductive layer 411 a or 411 b. Thus, the layout area of theconductive layer 401 can be large. That is, the aperture ratio can beincreased. Alternatively, a gate signal line (a wiring having a functionof supplying a signal for selecting a pixel) can be provided so as tooverlap with the conductive layer 404 or 405. Thus, the layout area ofthe conductive layer 401 can be large. That is, the aperture ratio canbe increased.

In the case where the conductive layers 411 a and 411 b extend in the Xdirection and the conductive layers 412 a and 412 b extend in the Ydirection in FIG. 26 or FIG. 28 , the directions in which the conductivelayers extend are changed; thus, the conductive layers 412 a and 412 bare provided so as not to overlap with the gate signal line but tooverlap with the source signal line, whereas the conductive layers 411 aand 411 b are provided so as not to overlap with the source signal linebut to overlap with the gate signal line.

In the case where the resistance of the conductive layers 411 a, 411 b,and 404 is desired to be reduced, low-resistance conductive layers 411a_1, 411 b_1, and 404_1 may be provided above or below the conductivelayers 411 a, 411 b, and 404, respectively. For example, a layer ofaluminum, copper, titanium, molybdenum, or tungsten, or a stacked layerof any of these metals may be provided above or below the conductivelayers 411 a, 411 b, and 404. Alternatively, at least one of theconductive layers 411 a_1, 411 b_1, and 404_1 may be formed of a meshedmetal film. Alternatively, at least one of the conductive layers 411a_1, 411 b_1, and 404_1 may be formed using a metal nanowire, a carbonnanotube, or the like. The conductive layer 401 preferably has alight-transmitting property. Therefore, it is preferable that alow-resistance conductive layer be not provided above or below theconductive layer 401. An example in that case is illustrated in FIG. 31and FIG. 32 .

In the case where the resistance values of the conductive layers 411 aand 411 b are desired to be substantially reduced, conductive layers 411aa and 411 bb may be provided. The conductive layer 411 a (theconductive layer 411 b) is connected to the conductive layer 411 aa (theconductive layer 411 bb) through a contact hole. An example in that caseis illustrated in FIG. 33 and FIG. 34 .

Note that only the conductive layer 405 may be formed separately but ispreferably formed at the same time as other conductive layers.

Structure Example 2-2

FIG. 35 illustrates an example in which the conductive layers 411 a, 411b, and 404 are formed by processing the same conductive film as theconductive layer 402. Therefore, the conductive layers 411 a, 411 b,404, and 402 are provided on the same plane. FIG. 36 is a schematiccross-sectional view of the touch panel, including the cross sectionalong the section line X3-X4 in FIG. 35 . FIG. 35 and FIG. 36 correspondto FIG. 8B.

As illustrated in FIG. 35 , the conductive layer 402 has anisland-shape. Like the conductive layers 412 a, the two adjacentconductive layers 402 which sandwich the conductive layer 411 a or 411 bare electrically connected to each other through the conductive layer405. Here is illustrated an example in which the two conductive layers402 adjacent to each other in the Y direction are not electricallyconnected to each other. However, the plurality of conductive layers 402may be electrically connected to each other through the conductive layer405 in the Y direction or both in the X direction and in the Ydirection. The case where the conductive layer 401 on the upper side isa pixel electrode and the conductive layer 402 on the lower side is acommon electrode is described in this example; however, the functions ofthese conductive layers may be reversed.

Alternatively, the conductive layer 405 may extend in the X direction asillustrated in FIG. 37 . In this manner, the wiring resistance of theconductive layer 404 can be substantially reduced.

Alternatively, in FIG. 35 or FIG. 37 , the conductive layers 411 a and411 b may extend in the X direction, and the conductive layers 412 a and412 b may extend in the Y direction.

In FIG. 36 , the conductive layer 405 is formed by processing the sameconductive film as the source and drain electrodes 285 of thetransistor. In that case, the layout of the conductive layer 405 has noproblem even when the gate electrode and the like are provided below theconductive layer 405. Thus, the conductive layer 405 can be provided soas to overlap with the gate electrode or a film formed by processing thesame conductive film as the gate electrode. However, one embodiment ofthe present invention is not limited thereto, and the conductive layer405 can be formed by processing the same conductive film as the gateelectrode 281, the semiconductor layer, or other conductive layers ofthe transistor.

FIG. 38 illustrates, as an example, the case where the conductive layer405 is formed by processing the same conductive film as the gateelectrode 281. In that case, the layout of the conductive layer 405 hasno problem even when the source and drain electrodes 285 and the likeare provided over the conductive layer 405. Thus, the conductive layer405 can be provided so as to overlap with or to cross the source anddrain electrodes 285 or a film formed by processing the same conductivefilm as the source and drain electrodes 285. That is, the source signalline can be provided so as to overlap with the conductive layer 411 a or411 b. Thus, the layout area of the conductive layer 401 can be large.That is, the aperture ratio can be increased.

FIG. 39 illustrates the case where the conductive layer 405 is formed byprocessing the same conductive film as the conductive layer 401. In thatcase, the layout of the conductive layer 405 has no problem even whenthe source and drain electrodes 285, the gate electrode, and the likeare provided below the conductive layer 405. Thus, the conductive layer405 can be provided so as to overlap with or to cross the gate electrodeor the source and drain electrodes 285, a film formed by processing thesame conductive film as the gate electrode, or a film formed byprocessing the same conductive film as the source and drain electrodes285. That is, the source signal line can be provided so as to overlapwith the conductive layer 411 a or 411 b. Thus, the layout area of theconductive layer 401 can be large. That is, the aperture ratio can beincreased. Alternatively, the gate signal line can be provided so as tooverlap with the conductive layer 404 or 405. Thus, the layout area ofthe conductive layer 401 can be large. That is, the aperture ratio canbe increased.

In the case where the conductive layers 411 a and 411 b extend in the Xdirection and the conductive layers 412 a and 412 b extend in the Ydirection in FIG. 35 or FIG. 37 , the directions in which the conductivelayers extend are changed; thus, the conductive layers 412 a and 412 bare provided so as not to overlap with the gate signal line but tooverlap with the source signal line, whereas the conductive layers 411 aand 411 b are provided so as not to overlap with the source signal linebut to overlap with the gate signal line.

FIG. 36 , FIG. 38 , and FIG. 39 each illustrate the example in which theconductive layer 401 on the upper side is a pixel electrode and theconductive layer 402 on the lower side is a common electrode. However,one embodiment of the present invention is not limited thereto. Theconductive layer 401 on the upper side may be a common electrode, andthe conductive layer 402 on the lower side may be a pixel electrode.Examples in that case are illustrated in FIG. 40 , FIG. 41 , and FIG. 42.

FIG. 40 , FIG. 41 , FIG. 42 , and the like each illustrate an example inwhich the conductive layers 411 a, 411 b, and 404 are formed byprocessing the same conductive film as the conductive layer 402.However, one embodiment of the present invention is not limited thereto.The conductive layers 411 a, 411 b, and 404 may also be formed byprocessing the same conductive film as the conductive layer 401.Therefore, the conductive layers 411 a, 411 b, 404, and 401 may also beprovided on the same plane. Examples in that case are illustrated inFIG. 43 , FIG. 44 , and FIG. 45 .

In the case where the resistance of the conductive layers 411 a, 411 b,and 404 is desired to be reduced, low-resistance conductive layers 411a_1, 411 b_1, and 404_1 may be provided above or below the conductivelayers 411 a, 411 b, and 404, respectively. For example, a layer ofaluminum, copper, titanium, molybdenum, or tungsten, or a stacked layerof any of these metals may be provided above or below the conductivelayers 411 a, 411 b, and 404. Alternatively, at least one of theconductive layers 411 a_1, 411 b_1, and 404_1 may be formed of a meshedmetal film. Alternatively, at least one of the conductive layers 411a_1, 411 b_1, and 404_1 may be formed using a metal nanowire, a carbonnanotube, or the like. The conductive layer 402 preferably has alight-transmitting property. Therefore, it is preferable that alow-resistance conductive layer be not provided above or below theconductive layer 402. An example in that case is illustrated in FIG. 46and FIG. 47 .

In the case where the resistance values of the conductive layers 411 aand 411 b are desired to be substantially reduced, the conductive layers411 aa and 411 bb may be provided. The conductive layer 411 a (theconductive layer 411 b) is connected to the conductive layer 411 aa (theconductive layer 411 bb) through a contact hole. An example in that caseis illustrated in FIG. 48 and FIG. 49 .

Structure Example 2-3

FIG. 50 illustrates an example in which the conductive layers 411 a and411 b are formed by processing the same conductive film as theconductive layer 401 and the conductive layers 412 a and 412 b areformed by processing the same conductive film as the conductive layer402. Therefore, the conductive layers 411 a, 411 b, and 401 are providedon the same plane. Similarly, the conductive layers 412 a, 412 b, and402 are provided on the same plane. FIG. 51 is a schematiccross-sectional view of the touch panel, including the cross sectionalong the section line X5-X6 in FIG. 50 . FIG. 50 and FIG. 51 correspondto FIG. 7E.

Two conductive layers functioning as a pair of electrodes of the touchsensor (such as the conductive layers 411 a and 412 a or the conductivelayers 411 b and 412 b) are formed in different layers as describedabove, in which case these two conductive layers can cross each other.Therefore, a bridge portion using the conductive layer 405 is notneeded, and the structure can be more simplified compared to thestructure examples 1 and 2. Accordingly, the manufacturing yield can beimproved. In addition, the layout of the conductive layer 411 a, 412 a,411 b, or 412 b has no problem even when the source and drain electrodes285, the gate electrode 281, and the like are provided below theconductive layer 411 a, 412 a, 411 b, or 412 b. Thus, the conductivelayer 411 a, 412 a, 411 b, or 412 b can be provided so as to overlapwith or to cross the gate electrode 281 or the source and drainelectrodes 285, a film formed by processing the same conductive film asthe gate electrode 281, or a film formed by processing the sameconductive film as the source and drain electrodes 285. That is, thesource signal line can be provided so as to overlap with the conductivelayer 411 a, 412 a, 411 b, or 412 b. Thus, the layout area of theconductive layer 401 can be large. That is, the aperture ratio can beincreased. Alternatively, the gate signal line can be provided so as tooverlap with the conductive layer 411 a, 412 a, 411 b, or 412 b. Thus,the layout area of the conductive layer 401 can be large. That is, theaperture ratio can be increased.

The case where the conductive layer 401 on the upper side is a pixelelectrode and the conductive layer 402 on the lower side is a commonelectrode is illustrated in FIG. 51 ; however, the functions of theseconductive layers may be reversed.

Alternatively, in FIG. 50 , the conductive layers 411 a and 411 b mayextend in the X direction, and the conductive layers 412 a and 412 b mayextend in the Y direction.

FIG. 50 and FIG. 51 each illustrate the example in which the conductivelayer 401 on the upper side is a pixel electrode and the conductivelayer 402 on the lower side is a common electrode. However, oneembodiment of the present invention is not limited thereto. Theconductive layer 401 on the upper side may be a common electrode, andthe conductive layer 402 on the lower side may be a pixel electrode. Anexample in that case is illustrated in FIG. 52 and FIG. 53 .

In the case where the resistance of the conductive layers 411 a, 411 b,412 a, and 412 b is desired to be reduced, low-resistance conductivelayers 411 a_1 and 411 b_1 and low-resistance conductive layers 412 a_1and 412 b_1 may be provided above or below the conductive layers 411 aand 411 b and the conductive layers 412 a and 412 b, respectively. Forexample, a layer of aluminum, copper, titanium, molybdenum, or tungsten,or a stacked layer of any of these metals may be provided above or belowthe conductive layers 411 a, 411 b, 412 a, and 412 b. Alternatively, atleast one of the conductive layers 411 a_1, 411 b_1, 412 a_1, and 412b_1 may be formed of a meshed metal film. Alternatively, at least one ofthe conductive layers 411 a_1, 411 b_1, 412 a_1, and 412 b_1 may beformed using a metal nanowire, a carbon nanotube, or the like. Theconductive layers 401 and 402 preferably have a light-transmittingproperty. Therefore, it is preferable that, in an opening, alow-resistance conductive layer be not provided above or below theconductive layers 401 and 402. An example in that case is illustrated inFIG. 54 and FIG. 55 .

In the case where the resistance values of the conductive layers 411 a,411 b, 412 a, and 412 b are desired to be substantially reduced, theconductive layers 411 aa and 411 bb and the conductive layers 412 aa and412 bb may be provided. The conductive layer 411 a (the conductive layer411 b, 412 a, or 412 b) is connected to the conductive layer 411 aa (theconductive layer 411 bb, 412 aa, or 412 bb) through a contact hole. Anexample in that case is illustrated in FIG. 56 and FIG. 57 . In the casewhere, for example, the conductive layer 411 a is connected to theconductive layer 411 aa, they may be connected through a hole providedin the conductive layer 402. That is, in the case where conductivelayers that are stacked with the conductive layer 402 providedtherebetween are connected to each other, a hole or the like is providedin the conductive layer 402.

Capacitance is formed at the intersection of the conductive layers 411 aand 411 b and the conductive layers 412 a and 412 b. In some cases,however, this capacitance is desired to be small. To reduce thiscapacitance formed at the intersection, the conductive layers may beconnected to each other through another conductive layer and a contacthole. An example in that case is illustrated in FIG. 58 and FIG. 59 . InFIG. 58 and FIG. 59 , the conductive layers 412 a (the conductive layers412 b) are connected to each other through a contact hole and theconductive layer 405. For example, the conductive layer 405 can beformed of a film formed by processing the same conductive film as thegate electrode 281 or a film formed by processing the same conductivefilm as the source and drain electrodes 285. In this manner, theparasitic capacitance due to the electrode in the touch sensor can bereduced. As a result, the sensitivity of the touch sensor can beimproved.

Structure Example 2-4

In the above structures, the pair of conductive layers of the liquidcrystal element and the pair of conductive layers of the touch sensorare provided separately. A structure in which one of the pair ofconductive layers of the liquid crystal element also serves as one ofthe pair of conductive layers of the touch sensor can also be employed.

FIG. 60 illustrates an example in which the conductive layers 402 eachhave a band-like shape extending in the X direction and are divided inthe Y direction. One of the conductive layers 402 functions as theconductive layer 412 a, 412 b, or 412 c having a function of theelectrode of the touch sensor and also functions as one of the pair ofconductive layers, e.g. the common electrode, of the liquid crystalelement. FIG. 61 is a schematic cross-sectional view of the touch panel,including the cross section along the section line X5-X6 in FIG. 60 .FIG. 60 and FIG. 61 correspond to FIG. 7C.

When the conductive layer (such as the conductive layer 412 a or 412 b)and the conductive layer 402 functioning as the pair of electrodes ofthe touch sensor are formed in different layers, these conductive layerscan cross each other. Therefore, a bridge portion using the conductivelayer 405 is not needed, and the structure can be more simplifiedcompared to the structure examples 1 and 2. Accordingly, themanufacturing yield can be improved. In addition, the layout of theconductive layer 411 a, 412 a, 411 b, or 412 b has no problem even whenthe source and drain electrodes 285, the gate electrode 281, and thelike are provided below the conductive layer 411 a, 412 a, 411 b, or 412b. Thus, the conductive layer 411 a, 412 a, 411 b, or 412 b can beprovided so as to overlap with or to cross the gate electrode 281 or thesource and drain electrodes 285, a film formed by processing the sameconductive film as the gate electrode 281, or a film formed byprocessing the same conductive film as the source and drain electrodes285. That is, the source signal line can be provided so as to overlapwith the conductive layer 411 a, 412 a, 411 b, or 412 b. Thus, thelayout area of the conductive layer 401 can be large. That is, theaperture ratio can be increased. Alternatively, the gate signal line canbe provided so as to overlap with the conductive layer 411 a, 412 a, 411b, or 412 b. Thus, the layout area of the conductive layer 401 can belarge. That is, the aperture ratio can be increased.

FIG. 60 and FIG. 61 each illustrate the example in which the conductivelayer 401 on the upper side is a pixel electrode and the conductivelayer 402 on the lower side is a common electrode. However, oneembodiment of the present invention is not limited thereto. Theconductive layer 401 on the upper side may be a common electrode, andthe conductive layer 402 on the lower side may be a pixel electrode. Anexample in that case is illustrated in FIG. 62 and FIG. 63 .

In the case where the resistance of the conductive layers 411 a, 411 b,412 a, and 412 b is desired to be reduced, low-resistance conductivelayers 411 a_1 and 411 b_1 and low-resistance conductive layers 412 a_1and 412 b_1 may be provided above or below the conductive layers 411 aand 411 b and the conductive layers 412 a and 412 b, respectively. Forexample, a layer of aluminum, copper, titanium, molybdenum, or tungsten,or a stacked layer of any of these metals may be provided above or belowthe conductive layers 411 a, 411 b, 412 a, and 412 b. Alternatively, atleast one of the conductive layers 411 a_1, 411 b_1, 412 a_1, and 412b_1 may be formed of a meshed metal film. Alternatively, at least one ofthe conductive layers 411 a_1, 411 b_1, 412 a_1, and 412 b_1 may beformed using a metal nanowire, a carbon nanotube, or the like. Theconductive layers 401 and 402 preferably have a light-transmittingproperty. Therefore, it is preferable that, in an opening, alow-resistance conductive layer be not provided above or below theconductive layers 401 and 402. An example in that case is illustrated inFIG. 64 and FIG. 65 .

In the case where the resistance values of the conductive layers 411 a,411 b, 412 a, and 412 b are desired to be substantially reduced, theconductive layers 411 aa and 411 bb and the conductive layers 412 aa and412 bb may be provided. The conductive layer 411 a (the conductive layer411 b, 412 a, or 412 b) is connected to the conductive layer 411 aa (theconductive layer 411 bb, 412 aa, or 412 bb) through a contact hole. Anexample in that case is illustrated in FIG. 66 and FIG. 67 . In the casewhere, for example, the conductive layer 411 a is connected to theconductive layer 411 aa, they may be connected through a hole providedin the conductive layer 402. That is, in the case where conductivelayers that are stacked with the conductive layer 402 providedtherebetween are connected to each other, a hole or the like is providedin the conductive layer 402.

Capacitance is formed at the intersection of the conductive layers 411 aand 411 b and the conductive layers 412 a and 412 b. In some cases,however, this capacitance is desired to be small. To reduce thiscapacitance formed at the intersection, the conductive layers may beconnected to each other through another conductive layer and a contacthole. An example in that case is illustrated in FIG. 68 and FIG. 69 . InFIG. 68 and FIG. 69 , the conductive layers 402 are connected to eachother through a contact hole and the conductive layer 405. For example,the conductive layer 405 can be formed of a film formed by processingthe same conductive film as the gate electrode 281 or a film formed byprocessing the same conductive film as the source and drain electrodes285. In this manner, the parasitic capacitance due to the electrode inthe touch sensor can be reduced. As a result, the sensitivity of thetouch sensor can be improved.

Alternatively, in FIG. 60 , the conductive layers 411 a and 411 b mayextend in the X direction, and the conductive layers 412 a and 412 b mayextend in the Y direction.

FIG. 70 illustrates an example in which the conductive layers 402 eachhave a band-like shape extending in the Y direction and are divided inthe X direction. One of the conductive layers 402 functions as theconductive layer 411 a, 411 b, or 411 c having a function of theelectrode of the touch sensor and also functions as one of the pair ofconductive layers, e.g. the common electrode, of the liquid crystalelement.

Such a structure is preferable because the structure of the touch panelcan be more simplified.

Although an example of the liquid crystal element using an FFS mode hasbeen described, for example, a structure with a liquid crystal elementusing an IPS mode can also be employed. In that case, the conductivelayers 401 and 402 may be formed by processing the same conductive film.Alternatively, both the conductive layers 401 and 402 may be formed tohave a comb-like shape when seen from the above. Alternatively, theconductive layer 402 functioning as a common electrode is preferablyformed into a band-like shape extending in the X direction or the Ydirection so as to function as one electrode of the touch sensor.

Structure Example 3

Structure examples of the touch panel partly different from thestructure examples 1 and 2 are described below with reference to thedrawings.

In a touch panel of one embodiment of the present invention which willbe described below, an organic EL element is used as a display element.

Structure Example 3-1

FIG. 71 illustrates a cross-sectional structure example of a regionincluding two sub-pixels. A touch panel illustrated in FIG. 71 includesa bottom emission light-emitting device which emits light through asubstrate that is provided with the transistor 201 and the like.

The touch panel includes a light-emitting element 202. Thelight-emitting element 202 includes a conductive layer 321, an EL layer322, and a conductive layer 323 which are stacked. An optical adjustmentlayer 324 may be provided between the conductive layer 321 and theconductive layer 323. Light is emitted from the light-emitting element202 through the substrate 371. An insulating layer 215 is provided so asto cover an end portion of the conductive layer 321 and an end portionof the optical adjustment layer 324.

The conductive layer 321 preferably has a light-transmitting property.The conductive layer 323 preferably has reflectivity.

The coloring layer 231 is provided closer to the substrate 371 than thelight-emitting element 202. In the structure illustrated in FIG. 71 ,the coloring layer 231 is provided over the insulating layer 213.

One of a conductive layer 351 and a conductive layer 352 functions asone electrode of the touch sensor, and the other functions as the otherelectrode of the touch sensor. The conductive layer 351 is formed on thesame plane as the conductive layer 321. The conductive layer 352 isformed on the same plane as one of two gate electrodes of the transistor201. Accordingly, the touch panel can be manufactured without anincrease in manufacturing steps.

As illustrated in FIG. 71 , detection can be performed by utilizing thecapacitance formed between the conductive layers 351 and 352 on thesubstrate 371 side.

[Light-Emitting Element]

As the light-emitting element, a self-luminous element can be used, andan element whose luminance is controlled by current or voltage isincluded in the category of the light-emitting element. For example, alight-emitting diode (LED), an organic EL element, an inorganic ELelement, or the like can be used.

The light-emitting element may be a top emission, bottom emission, ordual emission light-emitting element. A conductive film that transmitsvisible light is used as an electrode through which light is extracted.A conductive film that reflects visible light is preferably used as anelectrode through which light is not extracted.

The EL layer includes at least a light-emitting layer. In addition tothe light-emitting layer, the EL layer may further include one or morelayers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with a high electron- andhole-transport property), and the like.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer, and an inorganic compound may also be used. The layersincluded in the EL layer can be formed by any of the following methods:an evaporation method (including a vacuum evaporation method), atransfer method, a printing method, an inkjet method, a coating method,and the like.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between an anode and a cathode, holes are injected tothe EL layer from the anode side, and electrons are injected to the ELlayer from the cathode side. The injected electrons and holes arerecombined in the EL layer, so that a light-emitting substance containedin the EL layer emits light.

In the case where a light-emitting element emitting white light is usedas the light-emitting element, the EL layer preferably contains two ormore kinds of light-emitting substances. For example, light-emittingsubstances are selected so that two or more light-emitting substancesemit light of complementary colors to obtain white light emission.Specifically, it is preferable to contain two or more light-emittingsubstances selected from light-emitting substances emitting light of red(R), green (G), blue (B), yellow (Y), orange (O), and the like andlight-emitting substances emitting light containing two or more ofspectral components of R, G, and B. The light-emitting elementpreferably emits light with a spectrum having two or more peaks in thewavelength range of a visible light region (e.g., 350 nm to 750 nm). Anemission spectrum of a material emitting light having a peak in thewavelength range of yellow light preferably includes spectral componentsalso in the wavelength ranges of green light and red light.

More preferably, a light-emitting layer containing a light-emittingmaterial emitting light of one color and a light-emitting layercontaining a light-emitting material emitting light of another color arestacked in the EL layer. For example, the plurality of light-emittinglayers in the EL layer may be stacked in contact with each other or maybe stacked with a separation layer provided therebetween. For example,the separation layer may be provided between a fluorescent layer and aphosphorescent layer.

The separation layer can be provided, for example, to prevent energytransfer by the Dexter mechanism (particularly, triplet energy transfer)from a phosphorescent material or the like in an excited state which isgenerated in the phosphorescent layer to a fluorescent material or thelike in the fluorescent layer. The thickness of the separation layer maybe several nanometers. Specifically, the thickness of the separationlayer is greater than or equal to 0.1 nm and less than or equal to 20nm, greater than or equal to 1 nm and less than or equal to 10 nm, orgreater than or equal to 1 nm and less than or equal to 5 nm. Theseparation layer contains a single material (preferably, a bipolarsubstance) or a plurality of materials (preferably, a hole-transportmaterial and an electron-transport material).

The separation layer may be formed using a material contained in alight-emitting layer in contact with the separation layer. Thisfacilitates the manufacture of the light-emitting element and reducesthe drive voltage. For example, in the case where the phosphorescentlayer contains a host material, an assist material, and thephosphorescent material (a guest material), the separation layer maycontain the host material and the assist material. In other words, theseparation layer includes a region that does not contain thephosphorescent material, and the phosphorescent layer includes a regionthat contains the phosphorescent material in the above structure.Accordingly, the separation layer and the phosphorescent layer can beevaporated separately depending on whether the phosphorescent materialis contained or not. With such a structure, the separation layer and thephosphorescent layer can be formed in the same chamber. Thus, themanufacturing cost can be reduced.

The light-emitting element may be a single element including one ELlayer or a tandem element in which a plurality of EL layers are stackedwith a charge generation layer provided therebetween.

Structure Example 3-2

FIG. 72 is different from FIG. 71 in the position of the conductivelayer 352. In FIG. 72 , the conductive layer 352 and one of the gateelectrodes of the transistor 201 are provided between the insulatinglayer 212 and the insulating layer 213.

The conductive layer 352 and one of the gate electrodes of thetransistor 201 preferably include the low-resistance oxidesemiconductor.

As illustrated in FIG. 73 , the conductive layer 352 may be provided soas to overlap with at least one of the conductive layer 321, the opticaladjustment layer 324, the EL layer 322, the conductive layer 323, andthe coloring layer 231. As illustrated in FIG. 74 , the conductive layer352 may be provided so as not to overlap with the conductive layer 321,the optical adjustment layer 324, the EL layer 322, the conductive layer323, and the coloring layer 231.

Cross-Sectional Structure Example 3-2

In an example illustrated in FIG. 75 , both the conductive layers 351and 352 included in the touch sensor are formed on the same plane as theconductive layer 321.

Here, detection can be performed by utilizing the capacitance formedbetween the conductive layer 351 in one sub-pixel and the conductivelayer 352 in another sub-pixel.

Cross-Sectional Structure Example 3-3

FIG. 76 illustrates a cross-sectional structure example of a touch panelincluding a top emission light-emitting device which emits light throughthe substrate 372.

In the light-emitting element 202, the conductive layer 321 hasreflectivity, and the conductive layer 323 has a light-transmittingproperty.

The conductive layer 323 includes an opening at least in a region whichoverlaps with part of the conductive layer 351. The conductive layer 323may have a slit or an opening, or may have a comb-like shape.

The conductive layers 351 and 352 are formed on the same plane as theconductive layer 321.

In the example illustrated in FIG. 76 , detection can be performed byutilizing the capacitance formed between the conductive layer 351 in onesub-pixel and the conductive layer 352 in another sub-pixel.

As illustrated in FIG. 77 , the conductive layer 323 can be used as theelectrode of the touch sensor. That is, detection can be performed byutilizing the capacitance formed between the conductive layers 351 and323.

FIG. 77 illustrates an example in which the EL layer 322 is formed by aseparate coloring method. In that case, an end portion of the EL layer322 is covered with the conductive layer 323 as illustrated in FIG. 77 ,so that the diffusion of impurities into the EL layer 322 can besuppressed, leading to a higher reliability. In the example illustratedin FIG. 77 , the coloring layer 231 and the like are not provided.

Other Structure Examples

Note that one embodiment of the present invention is not limited to theabove-described structures and can have various structures.

[Positions of Sensor Electrode and Wiring for Pixel]

For example, whether a source line (signal line) is positioned on theright side or the left side of a pixel can be determined depending onwhether the pixel is provided in an even-numbered column or anodd-numbered column. As a result, two source lines are adjacent to eachother. A conductive layer (electrode) for a touch sensor can be providedthereover. In a similar manner, gate lines of vertically adjacent pixelsare provided close to each other, and the electrode for the touch sensorcan be provided thereover. FIG. 78 illustrates an example in that case.Two source lines 81 and 82 are adjacent to each other, and two sourcelines 83 and 84 are adjacent to each other. In addition, two gate lines85 and 86 are adjacent to each other, and two gate lines 87 and 88 areadjacent to each other.

[Peripheral Circuit]

A peripheral circuit can be formed outside a substrate over which pixelsare formed. That is, a circuit for driving a touch sensor and a circuitfor driving a pixel can be separately formed. Note that one circuit canalso have both the functions.

A driver circuit for selecting one of the conductive layers (electrodes)in the X direction or one of the conductive layers (electrodes) in the Ydirection of the touch sensor can be formed with a TFT over a substrateover which pixels are formed.

The circuit for driving a touch sensor may be provided on the gatedriver side for driving a pixel or the source driver side.

An IC is preferably used as a circuit that has a sensing function and isone of two circuits, a circuit electrically connected to the conductivelayers (electrodes) in the X direction and a circuit electricallyconnected to the conductive layers (electrodes) in the Y direction, ofthe touch sensor. In that case, the conductive layers are preferablycontrolled with the IC via an FPC.

[Material for Conductive Layer (Electrode) of Touch Sensor]

At least one of the pair of conductive layers of the touch sensor ispreferably formed using the same material as the common electrode, thepixel electrode, or the like of the liquid crystal element.

Alternatively, at least one of the conductive layers of the touch sensormay be formed of a meshed metal film (also referred to as a metal mesh).

By providing a metal film directly on or below at least one of theconductive layer (electrode) in the X direction and the conductive layer(electrode) in the Y direction of the touch sensor, the resistance ofthe conductive layer can be reduced. In that case, a stacked structureof a conductive film including a metal oxide and a conductive filmincluding a metal is preferably used, because these conductive films canbe formed by a patterning technique using a half tone mask and thus theprocess can be simplified.

[Wiring for Connecting Conductive Layers (Electrodes) of Touch Sensor]

In a region of the touch sensor where the conductive layer in the Xdirection crosses the conductive layer in the Y direction, a bridgestructure for connecting conductive layers using another conductivelayer is formed in such a manner that, for example, by using aconductive layer on the same plane as the gate electrode of thetransistor, conductive layers in the X direction are connected in thelateral direction parallel to the gate line throughout the pixels.Alternatively, by using a conductive layer on the same plane as thesource electrode and the drain electrode of the transistor, theconductive layers in the Y direction are connected in the verticaldirection parallel to the source line throughout the pixels. In thatcase, a contact portion can be formed in the pixel. Alternatively, thesame conductive layer as the conductive layer functioning as the commonelectrode or a conductive layer on the same plane as the conductivelayer functioning as the pixel electrode may also be used.

[Conductive Layer (Electrode) of Touch Sensor and Conductive Layer(Electrode) of Liquid Crystal Element]

A conductive layer (electrode) having a slit on the upper side can beused as the pixel electrode, and a conductive layer (electrode) providedin a plurality of pixels on the lower side can be used as the commonelectrode.

Alternatively, a conductive layer (electrode) which is provided in aplurality of pixels and has a slit on the upper side can be used as thecommon electrode, and a conductive layer (electrode) provided in each ofthe plurality of pixels on the lower side can be used as the pixelelectrode.

The conductive layer in the X direction of the touch sensor can alsoserve as the conductive layer functioning as the pixel electrode or theconductive layer functioning as the common electrode. Alternatively, theconductive layer in the Y direction of the touch sensor can also serveas the conductive layer functioning as the pixel electrode or theconductive layer functioning as the common electrode.

In addition, the conductive layer in the X direction of the touch sensormay be one of a conductive layer to which a pulse voltage is applied anda conductive layer for sensing a current. In that case, the conductivelayer in the Y direction of the touch sensor may be the other of theconductive layers.

In a region of the touch sensor where the conductive layer in the Xdirection crosses the conductive layer in the Y direction, one of theseconductive layers can have a shape different from that in other regions.For example, in the case where only the conductive layer functioning asthe pixel electrode and a conductive layer on the same plane as theconductive layer functioning as the pixel electrode are used to form apair of conductive layers of the touch sensor, the conductive layerfunctioning as the common electrode on the lower side is not providedbelow the conductive layers of the touch sensor. However, with astructure in which all conductive layers functioning as the commonelectrode are not provided below the conductive layers of the touchsensor, the conductive layers functioning as the common electrode havean island-shape. Therefore, a shape with a slit is preferably used sothat two adjacent conductive layers functioning as the common electrodecan be partly connected to each other.

The conductive layer functioning as the common electrode may be providedin a plurality of pixels. For example, the conductive layer functioningas the common electrode may be electrically connected to a common wiringformed using a conductive layer on the same plane as the gate electrodeof the transistor. In that case, one conductive layer functioning as thecommon electrode may have an island-shape.

[Counter Substrate]

When a substrate (also referred to as a counter substrate) that facesthe substrate provided with the transistor and the like is provided withthe conductive layer in the X direction or the conductive layer in the Ydirection of the touch sensor, a light-blocking layer is preferablyprovided closer to the viewing side than the conductive layer.

In the case where the counter substrate is provided with one electrodeof a liquid crystal element (in the case of a liquid crystal elementusing a TN mode, an MVA mode, or the like), the one electrode of theliquid crystal element may have a slit in a region which overlaps withthe conductive layer of the touch sensor provided on the countersubstrate.

In the case where a pair of electrodes of a liquid crystal element areprovided over a substrate over which a transistor and the like areprovided as in the case of a liquid crystal element using an FFS mode,an IPS mode, or the like, the counter substrate may be provided with aconductive layer for controlling the orientation of liquid crystal. In amanner similar to the above, the conductive layer for controlling theorientation of liquid crystal may also have a slit in a region whichoverlaps with the conductive layer of the touch sensor.

[Driving Method]

As a method for driving the touch sensor, for example, a method in whichsensing (scanning) of the corresponding row is performed in a periodbetween horizontal periods (gate selection periods) for the driving ofthe pixel can be used. Alternatively, one frame period may be divided intwo periods; writing to all pixels may be performed in the formerperiod, and sensing may be performed in the latter period.

[Transistor]

In this specification and the like, for example, a transistor with anyof a variety of structures can be used as the transistor, withoutlimitation to a certain type. For example, a transistor includingsingle-crystal silicon or a non-single-crystal semiconductor filmtypified by amorphous silicon, polycrystalline silicon, microcrystalline(also referred to as microcrystal, nanocrystal, or semi-amorphous)silicon, or the like can be used as the transistor. Alternatively, athin film transistor (TFT) whose semiconductor film is thinned or thelike can be used. In the case of using the TFT, there are variousadvantages. For example, since the TFT can be formed at a temperaturelower than that of the case of using single-crystal silicon, themanufacturing cost can be reduced or a manufacturing apparatus can bemade larger. Since the manufacturing apparatus is made larger, the TFTcan be formed using a large substrate. Therefore, many display devicescan be formed at the same time at low cost. In addition, a substratehaving low heat resistance can be used because of low manufacturingtemperature. Therefore, the transistor can be formed using alight-transmitting substrate. Transmission of light in a display elementcan be controlled by using the transistor formed using alight-transmitting substrate. In addition, part of a film included inthe transistor can transmit light because the thickness of thetransistor is small. Therefore, the aperture ratio can be improved.

Note that when a catalyst (e.g., nickel) is used in the case of formingpolycrystalline silicon, crystallinity can further be improved, and atransistor having excellent electric characteristics can be formed.Accordingly, a gate driver circuit (a scan line driver circuit), asource driver circuit (a signal line driver circuit), and a signalprocessing circuit (e.g., a signal generation circuit, a gammacorrection circuit, or a DA converter circuit) can be formed over asubstrate over which pixels are formed.

Note that when a catalyst (e.g., nickel) is used in the case of formingmicrocrystalline silicon, crystallinity can further be improved, and atransistor having excellent electric characteristics can be formed. Inthat case, crystallinity can be improved by just performing heattreatment without performing laser irradiation. Accordingly, a gatedriver circuit (a scan line driver circuit) and part of a source drivercircuit (an analog switch) can be formed over a substrate over whichpixels are formed. Note that when laser irradiation for crystallizationis not performed, unevenness in crystallinity of silicon can besuppressed. Therefore, high-quality images can be displayed. Note thatit is possible to form polycrystalline silicon or microcrystallinesilicon without a catalyst (e.g., nickel).

Note that although crystallinity of silicon is preferably improved topolycrystal, microcrystal, or the like in the whole panel, oneembodiment of the present invention is not limited thereto.Crystallinity of silicon may be improved only in part of the panel.Selective increase in crystallinity can be achieved by selective laserirradiation or the like. For example, only a peripheral circuit regionexcluding pixels may be irradiated with laser light. Alternatively, onlya region of a gate driver circuit, a source driver circuit, or the likemay be irradiated with laser light. Alternatively, only part of a sourcedriver circuit (e.g., an analog switch) may be irradiated with laserlight. Accordingly, crystallinity of silicon can be improved only in aregion where a circuit needs to operate at high speed. Since a pixelregion is not particularly needed to operate at high speed, even ifcrystallinity is not improved, the pixel circuit can operate withoutproblems. Thus, a region whose crystallinity is improved is small, sothat manufacturing steps can be decreased. Thus, throughput can beincreased and the manufacturing cost can be reduced. Alternatively,since the number of necessary manufacturing apparatuses is small, themanufacturing cost can be reduced.

Examples of the transistor include a transistor including a compoundsemiconductor (e.g., SiGe or GaAs) or an oxide semiconductor (e.g.,Zn—O, In—Ga—Zn—O, In—Zn—O, In—Sn—O (ITO), Sn—O, Ti—O, Al—Zn—Sn—O (AZTO),or In—Sn—Zn—O) and a thin film transistor including a thin film of sucha compound semiconductor or oxide semiconductor. Since manufacturingtemperature can be lowered, such a transistor can be formed at roomtemperature, for example. Accordingly, the transistor can be formeddirectly over a substrate having low heat resistance, such as a plasticsubstrate or a film substrate. Note that such a compound semiconductoror oxide semiconductor can be used not only for a channel portion of thetransistor but also for other applications. For example, such a compoundsemiconductor or oxide semiconductor can be used for a wiring, aresistor, a pixel electrode, a light-transmitting electrode, or thelike. Since such an element can be formed at the same time as thetransistor, cost can be reduced.

Note that for example, a transistor or the like formed by an inkjetmethod or a printing method can be used as the transistor. Accordingly,the transistor can be formed at room temperature, can be formed at a lowvacuum, or can be formed using a large substrate. Therefore, thetransistor can be formed without use of a mask (reticle), so that thelayout of the transistor can be easily changed. Alternatively, since thetransistor can be formed without use of a resist, the material cost isreduced, and the number of steps can be reduced. Furthermore, since afilm can be formed where needed, a material is not wasted compared to amanufacturing method by which etching is performed after the film isformed over the entire surface; thus, cost can be reduced.

Note that for example, a transistor or the like including an organicsemiconductor or a carbon nanotube can be used as the transistor. Such atransistor can be formed using a substrate which can be bent. A deviceincluding a transistor which includes an organic semiconductor or acarbon nanotube can resist a shock.

Note that a transistor with any of a variety of other structures canalso be used as the transistor. For example, a MOS transistor, ajunction transistor, a bipolar transistor, or the like can be used asthe transistor. By using a MOS transistor as the transistor, the size ofthe transistor can be reduced. Thus, a large number of transistors canbe mounted. By using a bipolar transistor as the transistor, a largeamount of current can flow. Thus, a circuit can operate at high speed.Note that a MOS transistor and a bipolar transistor may be formed overone substrate. Thus, a reduction in power consumption, a reduction insize, high speed operation, and the like can be realized.

Note that in this specification and the like, for example, a transistorwith a multi-gate structure having two or more gate electrodes can beused as the transistor. With the multi-gate structure, a structure inwhich a plurality of transistors are connected in series is providedbecause channel regions are connected in series. Thus, with themulti-gate structure, the amount of off-state current can be reduced,and the withstand voltage of the transistor can be increased (thereliability can be improved). Alternatively, with the multi-gatestructure, drain-source current does not change very much even ifdrain-source voltage changes when the transistor operates in asaturation region, so that a flat slope of voltage-currentcharacteristics can be obtained. By utilizing the flat slope of thevoltage-current characteristics, an ideal current source circuit or anactive load having an extremely high resistance value can be realized.Accordingly, a differential circuit, a current mirror circuit, or thelike having excellent properties can be realized.

Note that, for example, a transistor with a structure in which gateelectrodes are formed above and below a channel can be used as thetransistor. With the structure in which the gate electrodes are formedabove and below the channel, a circuit structure in which a plurality oftransistors are connected in parallel is provided. Thus, a channelregion is increased, so that the amount of current can be increased.Alternatively, by using the structure in which the gate electrodes areformed above and below the channel, a depletion layer can be easilyformed, so that subthreshold swing can be improved.

Note that as the transistor, for example, it is possible to use atransistor with a structure in which a gate electrode is formed above achannel region, a structure in which a gate electrode is formed below achannel region, a staggered structure, an inverted staggered structure,a structure in which a channel region is divided into a plurality ofregions, a structure in which channel regions are connected in parallelor in series, or the like. A transistor with any of a variety ofstructures such as a planar type, a FIN-type, a Tri-Gate type, atop-gate type, a bottom-gate type, a double-gate type (with gates aboveand below a channel), and the like can be used.

Note that for example, a transistor with a structure in which a sourceelectrode or a drain electrode overlaps with a channel region (or partof it) can be used as the transistor. By using the structure in whichthe source electrode or the drain electrode overlaps with the channelregion (or part of it), unstable operation due to accumulation ofelectric charge in part of the channel region can be prevented.

Note that for example, a transistor with a structure in which an LDDregion is provided can be used as the transistor. By providing the LDDregion, the amount of off-state current can be reduced or the withstandvoltage of the transistor can be increased (the reliability can beimproved). Alternatively, by providing the LDD region, drain currentdoes not change very much even if drain-source voltage changes when thetransistor operates in a saturation region, so that a flat slope ofvoltage-current characteristics can be obtained.

For example, FIG. 79 illustrates the case where a top-gate transistor isused in the structure of FIG. 61 .

[Connection]

For example, in this specification and the like, an explicit description“X and Y are connected” means that X and Y are electrically connected, Xand Y are functionally connected, and X and Y are directly connected.Accordingly, another element may be provided between elements having aconnection relation illustrated in drawings and texts, withoutlimitation on a predetermined connection relation, for example, theconnection relation illustrated in the drawings and the texts.

Here, X and Y each denote an object (e.g., a device, an element, acircuit, a wiring, an electrode, a terminal, a conductive film, or alayer).

Examples of the case where X and Y are directly connected include thecase where an element that allows an electrical connection between X andY (e.g., a switch, a transistor, a capacitor, an inductor, a resistor, adiode, a display element, a light-emitting element, or a load) is notconnected between X and Y, and the case where X and Y are connectedwithout the element that allows the electrical connection between X andY provided therebetween.

For example, in the case where X and Y are electrically connected, oneor more elements that enable electrical connection between X and Y(e.g., a switch, a transistor, a capacitor, an inductor, a resistor, adiode, a display element, a light-emitting element, or a load) can beconnected between X and Y A switch is controlled to be on or off. Thatis, a switch is conducting or not conducting (is turned on or off) todetermine whether current flows therethrough or not. Alternatively, theswitch has a function of selecting and changing a current path. Notethat the case where X and Y are electrically connected includes the casewhere X and Y are directly connected.

For example, in the case where X and Y are functionally connected, oneor more circuits that enable functional connection between X and Y(e.g., a logic circuit such as an inverter, a NAND circuit, or a NORcircuit; a signal converter circuit such as a DA converter circuit, anAD converter circuit, or a gamma correction circuit; a potential levelconverter circuit such as a power supply circuit (e.g., a step-upcircuit or a step-down circuit) or a level shifter circuit for changingthe potential level of a signal; a voltage source; a current source; aswitching circuit; an amplifier circuit such as a circuit that canincrease signal amplitude, the amount of current, or the like, anoperational amplifier, a differential amplifier circuit, a sourcefollower circuit, or a buffer circuit; a signal generation circuit; amemory circuit; and a control circuit) can be connected between X and Y.For example, when a signal output from X is transmitted to Y, it can besaid that X and Y are functionally connected even if another circuit isprovided between X and Y. Note that the case where X and Y arefunctionally connected includes the case where X and Y are directlyconnected and the case where X and Y are electrically connected.

Note that in this specification and the like, an explicit description “Xand Y are electrically connected” means that X and Y are electricallyconnected (i.e., the case where X and Y are connected with anotherelement or another circuit provided therebetween), X and Y arefunctionally connected (i.e., the case where X and Y are functionallyconnected with another circuit provided therebetween), and X and Y aredirectly connected (i.e., the case where X and Y are connected withoutanother element or another circuit provided therebetween). That is, inthis specification and the like, the explicit description “X and Y areelectrically connected” is the same as the description “X and Y areconnected”.

Note that, for example, the case where a source (or a first terminal orthe like) of a transistor is electrically connected to X through (or notthrough) Z1 and a drain (or a second terminal or the like) of thetransistor is electrically connected to Y through (or not through) Z2,or the case where a source (or a first terminal or the like) of atransistor is directly connected to one part of Z1 and another part ofZ1 is directly connected to X while a drain (or a second terminal or thelike) of the transistor is directly connected to one part of Z2 andanother part of Z2 is directly connected to Y, can be expressed by usingany of the following expressions.

Example of the expression include “X, Y, a source (or a first terminalor the like) of a transistor, and a drain (or a second terminal or thelike) of the transistor are electrically connected to each other, and X,the source (or the first terminal or the like) of the transistor, thedrain (or the second terminal or the like) of the transistor, and Y areelectrically connected to each other in this order”, “a source (or afirst terminal or the like) of a transistor is electrically connected toX, a drain (or a second terminal or the like) of the transistor iselectrically connected to Y, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are electrically connected to each otherin this order”, and “X is electrically connected to Y through a source(or a first terminal or the like) and a drain (or a second terminal orthe like) of a transistor, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are provided to be connected to eachother in this order”. When the connection order in a circuitconfiguration is defined by an expression similar to the above examples,a source (or a first terminal or the like) and a drain (or a secondterminal or the like) of a transistor can be distinguished from eachother to specify the technical scope.

Other examples of the expression include “a source (or a first terminalor the like) of a transistor is electrically connected to X through atleast a first connection path, the first connection path does notinclude a second connection path, the second connection path is a pathbetween the source (or the first terminal or the like) of the transistorand a drain (or a second terminal or the like) of the transistor, Z1 ison the first connection path, the drain (or the second terminal or thelike) of the transistor is electrically connected to Y through at leasta third connection path, the third connection path does not include thesecond connection path, and Z2 is on the third connection path” and “asource (or a first terminal or the like) of a transistor is electricallyconnected to X at least with a first connection path through Z1, thefirst connection path does not include a second connection path, thesecond connection path includes a connection path through thetransistor, a drain (or a second terminal or the like) of the transistoris electrically connected to Y at least with a third connection paththrough Z2, and the third connection path does not include the secondconnection path”. Still another example of the expression is “a source(or a first terminal or the like) of a transistor is electricallyconnected to X through at least Z1 on a first electrical path, the firstelectrical path does not include a second electrical path, the secondelectrical path is an electrical path from the source (or the firstterminal or the like) of the transistor to a drain (or a second terminalor the like) of the transistor, the drain (or the second terminal or thelike) of the transistor is electrically connected to Y through at leastZ2 on a third electrical path, the third electrical path does notinclude a fourth electrical path, and the fourth electrical path is anelectrical path from the drain (or the second terminal or the like) ofthe transistor to the source (or the first terminal or the like) of thetransistor”. When the connection path in a circuit configuration isdefined by an expression similar to the above examples, a source (or afirst terminal or the like) and a drain (or a second terminal or thelike) of a transistor can be distinguished from each other to specifythe technical scope.

Note that these expressions are examples and there is no limitation onthe expressions. Here, X, Y, Z1, and Z2 each denote an object (e.g., adevice, an element, a circuit, a wiring, an electrode, a terminal, aconductive film, or a layer).

Even when independent components are electrically connected to eachother in a circuit diagram, one component has functions of a pluralityof components in some cases. For example, when part of a wiring alsofunctions as an electrode, one conductive film functions as the wiringand the electrode. Thus, “electrical connection” in this specificationincludes, in its category, such a case where one conductive film hasfunctions of a plurality of components.

[Substrate]

Note that in this specification and the like, a transistor can be formedusing any of a variety of substrates, for example. The type of asubstrate is not limited to a certain type. Examples of the substrateinclude a semiconductor substrate (e.g., a single crystal substrate or asilicon substrate), an SOI substrate, a glass substrate, a quartzsubstrate, a plastic substrate, a sapphire glass substrate, a metalsubstrate, a stainless steel substrate, a substrate including stainlesssteel foil, a tungsten substrate, a substrate including tungsten foil, aflexible substrate, an attachment film, paper including a fibrousmaterial, a base film, and the like. Examples of a glass substrateinclude a barium borosilicate glass substrate, an aluminoborosilicateglass substrate, and a soda lime glass substrate. Examples of theflexible substrate, the attachment film, the base film, and the likeinclude substrates of plastics typified by polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polyether sulfone (PES), andpolytetrafluoroethylene (PTFE). Another example is a synthetic resinsuch as acrylic. Other examples are polypropylene, polyester, polyvinylfluoride, and polyvinyl chloride. Other examples are polyamide,polyimide, aramid, epoxy, an inorganic vapor deposition film, and paper.Specifically, the use of a semiconductor substrate, a single crystalsubstrate, an SOI substrate, or the like enables the manufacture ofsmall-sized transistors with a small variation in characteristics, size,shape, or the like and with high current capability. A circuit usingsuch transistors achieves lower power consumption or higher integration.

Alternatively, a flexible substrate may be used as the substrate, andthe transistor may be formed directly over the flexible substrate.Further alternatively, a separation layer may be provided between thesubstrate and the transistor. The separation layer can be used when partor the whole of a semiconductor device formed over the separation layeris separated from the substrate and transferred to another substrate. Insuch a case, the transistor can be transferred to a substrate having lowheat resistance or a flexible substrate as well. For the aboveseparation layer, a stack including inorganic films, a tungsten film anda silicon oxide film, or an organic resin film of polyimide or the likeformed over a substrate can be used, for example.

In other words, a transistor may be formed using one substrate and thentransferred to another substrate. Examples of a substrate to which atransistor is transferred include, in addition to the above substrateover which the transistor can be formed, a paper substrate, a cellophanesubstrate, an aramid film substrate, a polyimide film substrate, a stonesubstrate, a wood substrate, a cloth substrate (including a naturalfiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon,polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra,rayon, or regenerated polyester), and the like), a leather substrate,and a rubber substrate. When such a substrate is used, a transistor withexcellent properties or a transistor with low power consumption can beformed, a device with high durability can be manufactured, high heatresistance can be provided, or a reduction in weight or thickness can beachieved.

At least part of this embodiment can be implemented in combination withany of the other embodiments or at least another part of this embodimentdescribed in this specification as appropriate.

Embodiment 2

In this embodiment, examples of the display device described in theabove embodiment in which a driver IC is used will be described withreference to FIGS. 80A and 80B.

A display device 500A illustrated in FIG. 80A includes a pixel portion510, a gate driver 520_1, a gate driver 520_2, and a source driver 530.The pixel portion 510 includes pixels 511 each connected to a gate lineGL and a source line SL. The source driver 530 includes a plurality ofTAB (tape automated bonding) tapes 531 and source driver ICs 532_1 to532_k (k is a natural number of 2 or more).

In the pixel portion 510, for example, the pixels 511 are provided in amatrix in the long-side direction (X direction in FIG. 80A) and theshort-side direction (Y direction in FIG. 80A). Therefore, in thestructure of this embodiment, the number of the pixels 511 which areconnected to the same source line SL and provided in the long-sidedirection is larger than the number of the pixels 511 which areconnected to the same gate line GL and provided in the short-sidedirection.

The gate driver 520_1 and the gate driver 520_2 are provided on twosides in the long-side direction. The gate driver 520_1 drives gatelines (GL1 and GL3) in odd-numbered rows, and the gate driver 520_2drives gate lines (GL2 and GL4) in even-numbered rows. The larger thenumber of the pixels, the larger the number of the gate lines GLarranged in the long-side direction. With the gate driver 520_1 and thegate driver 520_2, a selection period for one gate line GL can belonger.

The gate drivers 520_1 and 520_2 are not needed to operate at high speedcompared to the source driver 530. Therefore, the gate drivers 520_1 and520_2 each preferably include a transistor fabricated in a mannersimilar to that in the pixel 511. When the gate drivers 520_1 and 520_2are incorporated in the display device 500A, cost can be reduced. Inaddition, the display device 500A can have a narrower frame.

The source driver ICs 532_1 to 532_k (k is a natural number of 2 ormore) are mounted on the TAB tapes 531 with anisotropic conductiveadhesive or the like. The plurality of TAB tapes 531 mounted with thesource driver ICs 532_1 to 532_k are attached to the display device500A; in this way, the plurality of source lines (SL1 and SL2) aredriven.

The source driver ICs 532_1 to 532_k operate at higher speed than thegate drivers 520_1 and 520_2. Therefore, unlike the gate drivers 520_1and 520_2, the source driver ICs 532_1 to 532_k are incorporated intothe display device 500A with difficulty. When the source driver 530 isprovided on the short side as in this embodiment, the number of thesource driver ICs can be reduced, leading to a reduction in cost.

A reduction in the number of the source driver ICs is very effectiveparticularly for a display device with a large number of pixels, e.g., adisplay device with 8K×4K pixels. The display device with a large numberof pixels can be fabricated at low cost, which enables fabrication of adisplay device that has a high pixel resolution and can display morerealistic images at low cost.

FIG. 80B illustrates a structure different from the structure in FIG.80A. A display device 500B illustrated in FIG. 80B is different from thedisplay device in FIG. 80A in that the number of the gate lines GL forpixels in one row is increased and the number of the source lines SL forpixels in one column is reduced.

In FIG. 80B, the gate drivers 520_1 and 520_2 are provided on two sidesin the long-side direction as in FIG. 80A. The gate driver 520_1 drivesgate lines (GL1, GL3, GL5, and GL7) in odd-numbered rows, and the gatedriver 520_2 drives gate lines (GL2, GL4, GL6, and GL8) in even-numberedrows.

The source driver ICs 532_1 to 532_k/2 in FIG. 80B only have to drivethe source lines (e.g., SL1) whose number is a half of that in FIG. 80A.Accordingly, the number of the source driver ICs can further be reduced,leading to a further reduction in cost.

To achieve a display device whose screen diagonal is particularly 50inches or more, or 60 inches or more, a transistor in each pixelpreferably has a relatively high mobility. Although polycrystallinesilicon or the like can be used for a semiconductor layer of atransistor, an oxide semiconductor is preferably used for example,because the transistor can be easily formed over a large substrate. Inthe case of using an In-M-Zn oxide for the oxide semiconductor, an oxidecontaining a larger amount of In than that of M is preferably used. Forexample, an oxide semiconductor film in which an oxide film with a ratioof In:Ga:Zn=4:2:3 and an oxide film with a ratio of In:Ga:Zn=1:1:1 arestacked is used for the semiconductor layer of the transistor; in thisway, the transistor can have a high mobility.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 3

In this embodiment, an example of a transistor which can be used as thetransistor described in the above embodiment will be described withreference to the drawings.

The touch panel of one embodiment of the present invention can befabricated by using a transistor with any of various structures, such asa bottom-gate transistor, a top-gate transistor, or the like. Therefore,a material for a semiconductor layer or the structure of a transistorcan be easily changed depending on the existing production line.

[Bottom-Gate Transistor]

FIG. 81A1 is a cross-sectional view of a transistor 810 that is achannel-protective transistor, which is a type of bottom-gatetransistor. In FIG. 81A1, the transistor 810 is formed over a substrate771. The transistor 810 includes an electrode 746 over the substrate 771with an insulating layer 772 provided therebetween. The transistor 810includes a semiconductor layer 742 over the electrode 746 with aninsulating layer 726 provided therebetween. The electrode 746 canfunction as a gate electrode. The insulating layer 726 can function as agate insulating layer.

The transistor 810 includes an insulating layer 741 over a channelformation region in the semiconductor layer 742. The transistor 810includes an electrode 744 a and an electrode 744 b which are partly incontact with the semiconductor layer 742 and over the insulating layer726. The electrode 744 a can function as one of a source electrode and adrain electrode. The electrode 744 b can function as the other of thesource electrode and the drain electrode. Part of the electrode 744 aand part of the electrode 744 b are formed over the insulating layer741.

The insulating layer 741 can function as a channel protective layer.With the insulating layer 741 provided over the channel formationregion, the semiconductor layer 742 can be prevented from being exposedat the time of forming the electrodes 744 a and 744 b. Thus, the channelformation region in the semiconductor layer 742 can be prevented frombeing etched at the time of forming the electrodes 744 a and 744 b. Inaccordance with one embodiment of the present invention, a transistorwith favorable electrical characteristics can be provided.

The transistor 810 includes an insulating layer 728 over the electrode744 a, the electrode 744 b, and the insulating layer 741 and furtherincludes an insulating layer 729 over the insulating layer 728.

The electrode, the semiconductor layer, the insulating layer, and thelike used in the transistor disclosed in this embodiment can be formedusing a material and a method disclosed in any of the other embodiments.

In the case where an oxide semiconductor is used for the semiconductorlayer 742, a material capable of removing oxygen from part of thesemiconductor layer 742 to generate oxygen vacancies is preferably usedfor regions of the electrodes 744 a and 744 b that are in contact withat least the semiconductor layer 742. The carrier concentration in theregions of the semiconductor layer 742 where oxygen vacancies aregenerated is increased, so that the regions become n-type regions (n⁺layers). Accordingly, the regions can function as a source region and adrain region. When an oxide semiconductor is used for the semiconductorlayer 742, examples of the material capable of removing oxygen from thesemiconductor layer 742 to generate oxygen vacancies include tungstenand titanium.

Formation of the source region and the drain region in the semiconductorlayer 742 makes it possible to reduce contact resistance between thesemiconductor layer 742 and each of the electrodes 744 a and 744 b.Accordingly, the electric characteristics of the transistor, such as thefield-effect mobility and the threshold voltage, can be favorable.

In the case where a semiconductor such as silicon is used for thesemiconductor layer 742, a layer that functions as an n-typesemiconductor or a p-type semiconductor is preferably provided betweenthe semiconductor layer 742 and the electrode 744 a and between thesemiconductor layer 742 and the electrode 744 b. The layer thatfunctions as an n-type semiconductor or a p-type semiconductor canfunction as the source region or the drain region in the transistor.

The insulating layer 729 is preferably formed using a material that canprevent or reduce diffusion of impurities into the transistor from theoutside. The formation of the insulating layer 729 may also be omitted.

When an oxide semiconductor is used for the semiconductor layer 742,heat treatment may be performed before and/or after the insulating layer729 is formed. The heat treatment can fill oxygen vacancies in thesemiconductor layer 742 by diffusing oxygen contained in the insulatinglayer 729 or other insulating layers into the semiconductor layer 742.Alternatively, the insulating layer 729 may be formed while the heattreatment is performed, so that oxygen vacancies in the semiconductorlayer 742 can be filled.

Note that a CVD method can be generally classified into a plasmaenhanced CVD (PECVD) method using plasma, a thermal CVD (TCVD) methodusing heat, and the like. A CVD method can further be classified into ametal CVD (MCVD) method, a metal organic CVD (MOCVD) method, and thelike according to a source gas to be used.

Furthermore, an evaporation method can be generally classified into aresistance heating evaporation method, an electron beam evaporationmethod, a molecular beam epitaxy (MBE) method, a pulsed laser deposition(PLD) method, an ion beam assisted deposition (IAD) method, an atomiclayer deposition (ALD) method, and the like.

By using a PECVD method, a high-quality film can be formed at arelatively low temperature. By using a deposition method that does notuse plasma for deposition, such as an MOCVD method or an evaporationmethod, a film with few defects can be formed because damage is noteasily caused on a surface on which the film is deposited.

A sputtering method is generally classified into a DC sputtering method,a magnetron sputtering method, an RF sputtering method, an ion beamsputtering method, an electron cyclotron resonance (ECR) sputteringmethod, a facing-target sputtering method, and the like.

In a facing-target sputtering method, plasma is confined betweentargets; thus, plasma damage to a substrate can be reduced. Furthermore,step coverage can be improved because the incident angle of a sputteredparticle to a substrate can be made smaller depending on the inclinationof a target.

A transistor 811 illustrated in FIG. 81A2 is different from thetransistor 810 in that an electrode 723 that can function as a back gateelectrode is provided over the insulating layer 729. The electrode 723can be formed using a material and a method similar to those of theelectrode 746.

In general, a back gate electrode is formed using a conductive layer andpositioned so that a channel formation region of a semiconductor layeris positioned between a gate electrode and the back gate electrode.Thus, the back gate electrode can function in a manner similar to thatof the gate electrode. The potential of the back gate electrode may bethe same as that of the gate electrode or may be a ground (GND)potential or a predetermined potential. By changing the potential of theback gate electrode independently of the potential of the gateelectrode, the threshold voltage of the transistor can be changed.

The electrode 746 and the electrode 723 can each function as a gateelectrode. Thus, the insulating layers 726, 728, and 729 can eachfunction as a gate insulating layer. The electrode 723 may also beprovided between the insulating layers 728 and 729.

In the case where one of the electrode 746 and the electrode 723 issimply referred to as a “gate electrode”, the other can be referred toas a “back gate electrode”. For example, in the transistor 811, in thecase where the electrode 723 is referred to as a “gate electrode”, theelectrode 746 is referred to as a “back gate electrode”. In the casewhere the electrode 723 is used as a “gate electrode”, the transistor811 is a kind of top-gate transistor. Alternatively, one of theelectrode 746 and the electrode 723 may be referred to as a “first gateelectrode”, and the other may be referred to as a “second gateelectrode”.

By providing the electrode 746 and the electrode 723 with thesemiconductor layer 742 provided therebetween and setting the potentialsof the electrode 746 and the electrode 723 to be the same, a region ofthe semiconductor layer 742 through which carriers flow is enlarged inthe film thickness direction; thus, the number of transferred carriersis increased. As a result, the on-state current and field-effectmobility of the transistor 811 are increased.

Therefore, the transistor 811 has a comparatively high on-state currentfor its area. That is, the area of the transistor 811 can be small for arequired on-state current. In accordance with one embodiment of thepresent invention, the area of a transistor can be reduced. Therefore,in accordance with one embodiment of the present invention, asemiconductor device having a high degree of integration can beprovided.

The gate electrode and the back gate electrode are formed usingconductive layers and thus each have a function of preventing anelectric field generated outside the transistor from influencing thesemiconductor layer in which the channel is formed (in particular, anelectric field blocking function against static electricity and thelike). When the back gate electrode is formed larger than thesemiconductor layer such that the semiconductor layer is covered withthe back gate electrode, the electric field blocking function can beenhanced.

Since the electrode 746 and the electrode 723 each have a function ofblocking an electric field generated outside, electric charge of chargedparticles and the like generated on the insulating layer 772 side orabove the electrode 723 do not influence the channel formation region inthe semiconductor layer 742. Thus, degradation by a stress test (e.g., anegative gate bias temperature (−GBT) stress test in which negativeelectric charge is applied to a gate) can be reduced. Furthermore, achange in gate voltage (rising voltage) at which on-state current startsflowing depending on drain voltage can be reduced. Note that this effectis obtained when the electrodes 746 and 723 have the same potential ordifferent potentials.

The BT stress test is one kind of acceleration test and can evaluate, ina short time, a change by long-term use (i.e., a change over time) incharacteristics of a transistor. In particular, the amount of change inthreshold voltage of a transistor before and after the BT stress test isan important indicator when examining the reliability of the transistor.As the change in the threshold voltage is smaller, the transistor hashigher reliability.

By providing the electrodes 746 and 723 and setting the potentials ofthe electrodes 746 and 723 to be the same, the amount of change inthreshold voltage is reduced. Accordingly, variations in electricalcharacteristics among a plurality of transistors are also reduced.

A transistor including a back gate electrode has a smaller change inthreshold voltage before and after a positive GBT stress test, in whichpositive electric charge is applied to a gate, than a transistorincluding no back gate electrode.

When the back gate electrode is formed using a light-blocking conductivefilm, light can be prevented from entering the semiconductor layer fromthe back gate electrode side. Therefore, photodegradation of thesemiconductor layer can be prevented, and deterioration in electricalcharacteristics of the transistor, such as a shift of the thresholdvoltage, can be prevented.

In accordance with one embodiment of the present invention, a transistorwith high reliability can be provided. Moreover, a semiconductor devicewith high reliability can be provided.

FIG. 81B1 is a cross-sectional view of a channel-protective transistor820 that is a type of bottom-gate transistor. The transistor 820 hassubstantially the same structure as the transistor 810 but is differentfrom the transistor 810 in that the insulating layer 741 covers thesemiconductor layer 742. The semiconductor layer 742 is electricallyconnected to the electrode 744 a through an opening formed byselectively removing part of the insulating layer 741 which overlapswith the semiconductor layer 742. The semiconductor layer 742 iselectrically connected to the electrode 744 b through another openingformed by selectively removing part of the insulating layer 741 whichoverlaps with the semiconductor layer 742. A region of the insulatinglayer 741 which overlaps with the channel formation region can functionas a channel protective layer.

A transistor 821 illustrated in FIG. 81B2 is different from thetransistor 820 in that the electrode 723 that can function as a backgate electrode is provided over the insulating layer 729.

With the insulating layer 741, the semiconductor layer 742 can beprevented from being exposed at the time of forming the electrodes 744 aand 744 b. Thus, the semiconductor layer 742 can be prevented from beingreduced in thickness at the time of forming the electrodes 744 a and 744b.

The length between the electrode 744 a and the electrode 746 and thelength between the electrode 744 b and the electrode 746 in thetransistors 820 and 821 are larger than those in the transistors 810 and811. Thus, the parasitic capacitance generated between the electrode 744a and the electrode 746 can be reduced. Moreover, the parasiticcapacitance generated between the electrode 744 b and the electrode 746can be reduced. In accordance with one embodiment of the presentinvention, a transistor with favorable electrical characteristics can beprovided.

A transistor 825 illustrated in FIG. 81C1 is a channel-etched transistorthat is a type of bottom-gate transistor. In the transistor 825, theelectrodes 744 a and 744 b are formed without providing the insulatinglayer 741. Thus, part of the semiconductor layer 742 that is exposed atthe time forming the electrodes 744 a and 744 b is etched in some cases.However, since the insulating layer 741 is not provided, theproductivity of the transistor can be increased.

A transistor 826 illustrated in FIG. 81C2 is different from thetransistor 825 in that the electrode 723 which can function as a backgate electrode is provided over the insulating layer 729.

[Top-Gate Transistor]

FIG. 82A1 is a cross-sectional view of a transistor 830 that is a typeof top-gate transistor. The transistor 830 includes the semiconductorlayer 742 over the insulating layer 772, the electrodes 744 a and 744 bthat are over the semiconductor layer 742 and the insulating layer 772and in contact with part of the semiconductor layer 742, the insulatinglayer 726 over the semiconductor layer 742 and the electrodes 744 a and744 b, and the electrode 746 over the insulating layer 726.

Since the electrode 746 overlaps with neither the electrode 744 a northe electrode 744 b in the transistor 830, the parasitic capacitancegenerated between the electrodes 746 and 744 a and the parasiticcapacitance generated between the electrodes 746 and 744 b can bereduced. After the formation of the electrode 746, an impurity 755 isintroduced into the semiconductor layer 742 using the electrode 746 as amask, so that an impurity region can be formed in the semiconductorlayer 742 in a self-aligned manner (see FIG. 82A3). In accordance withone embodiment of the present invention, a transistor with favorableelectrical characteristics can be provided.

The introduction of the impurity 755 can be performed with an ionimplantation apparatus, an ion doping apparatus, or a plasma treatmentapparatus.

As the impurity 755, for example, at least one kind of element of Group13 elements and Group 15 elements can be used. In the case where anoxide semiconductor is used for the semiconductor layer 742, it ispossible to use at least one kind of element of a rare gas, hydrogen,and nitrogen as the impurity 755.

A transistor 831 illustrated in FIG. 82A2 is different from thetransistor 830 in that the electrode 723 and the insulating layer 727are included. The transistor 831 includes the electrode 723 formed overthe insulating layer 772 and the insulating layer 727 formed over theelectrode 723. The electrode 723 can function as a back gate electrode.Thus, the insulating layer 727 can function as a gate insulating layer.The insulating layer 727 can be formed using a material and a methodsimilar to those of the insulating layer 726.

Like the transistor 811, the transistor 831 has a high on-state currentfor its area. That is, the area of the transistor 831 can be small for arequired on-state current. In accordance with one embodiment of thepresent invention, the area of a transistor can be reduced. Therefore,in accordance with one embodiment of the present invention, asemiconductor device having a high degree of integration can beprovided.

A transistor 840 illustrated in FIG. 82B1 is a type of top-gatetransistor. The transistor 840 is different from the transistor 830 inthat the semiconductor layer 742 is formed after the formation of theelectrodes 744 a and 744 b. A transistor 841 illustrated in FIG. 82B2 isdifferent from the transistor 840 in that the electrode 723 and theinsulating layer 727 are included. In the transistors 840 and 841, partof the semiconductor layer 742 is formed over the electrode 744 a andanother part of the semiconductor layer 742 is formed over the electrode744 b.

Like the transistor 811, the transistor 841 has a high on-state currentfor its area. That is, the area of the transistor 841 can be small for arequired on-state current. In accordance with one embodiment of thepresent invention, the area of a transistor can be reduced. Therefore,in accordance with one embodiment of the present invention, asemiconductor device having a high degree of integration can beprovided.

A transistor 842 illustrated in FIG. 83A1 is a type of top-gatetransistor. The transistor 842 is different from the transistor 830 or840 in that the electrodes 744 a and 744 b are formed after theformation of the insulating layer 729. The electrodes 744 a and 744 bare electrically connected to the semiconductor layer 742 throughopenings formed in the insulating layers 728 and 729.

Part of the insulating layer 726 that does not overlap with theelectrode 746 is removed, and the impurity 755 is introduced into thesemiconductor layer 742 using the electrode 746 and the insulating layer726 that is left as a mask, so that an impurity region can be formed inthe semiconductor layer 742 in a self-aligned manner (see FIG. 83A3).The transistor 842 includes a region where the insulating layer 726extends beyond an end portion of the electrode 746. The semiconductorlayer 742 in a region into which the impurity 755 is introduced throughthe insulating layer 726 has a lower impurity concentration than thesemiconductor layer 742 in a region into which the impurity 755 isintroduced without through the insulating layer 726. Thus, a lightlydoped drain (LDD) region is formed in a region adjacent to a region ofthe semiconductor layer 742 which overlaps with the electrode 746.

A transistor 843 illustrated in FIG. 83A2 is different from thetransistor 842 in that the electrode 723 is included. The transistor 843includes the electrode 723 that is formed over the substrate 771 andoverlaps with the semiconductor layer 742 with the insulating layer 772provided therebetween. The electrode 723 can function as a back gateelectrode.

As in a transistor 844 illustrated in FIG. 83B1 and a transistor 845illustrated in FIG. 83B2, the insulating layer 726 in a region that doesnot overlap with the electrode 746 may be completely removed.Alternatively, as in a transistor 846 illustrated in FIG. 83C1 and atransistor 847 illustrated in FIG. 83C2, the insulating layer 726 may beleft in a region which does not overlap with the electrode 746.

In the transistors 842 to 847, after the formation of the electrode 746,the impurity 755 is introduced into the semiconductor layer 742 usingthe electrode 746 as a mask, so that an impurity region can be formed inthe semiconductor layer 742 in a self-aligned manner. In accordance withone embodiment of the present invention, a transistor with favorableelectrical characteristics can be provided. Furthermore, in accordancewith one embodiment of the present invention, a semiconductor devicehaving a high degree of integration can be provided.

[S-Channel Transistor]

FIGS. 84A to 84C illustrate an example of the structure of a transistorusing an oxide semiconductor for the semiconductor layer 742. In atransistor 850 illustrated in FIGS. 84A to 84C, a semiconductor layer742 b is formed over a semiconductor layer 742 a, and a semiconductorlayer 742 c covers a top surface and a side surface of the semiconductorlayer 742 b and a side surface of the semiconductor layer 742 a. FIG.84A is a top view of the transistor 850. FIG. 84B is a cross-sectionalview (in the channel length direction) taken along the dashed-dottedline X1-X2 in FIG. 84A. FIG. 84C is a cross-sectional view (in thechannel width direction) taken along the dashed-dotted line Y1-Y2 inFIG. 84A.

The transistor 850 includes the electrode 743 functioning as a gateelectrode. The electrode 743 can be formed using a material and a methodsimilar to those of the electrode 746. The electrode 743 is formed oftwo conductive layers in this embodiment.

Each of the semiconductor layer 742 a, the semiconductor layer 742 b,and the semiconductor layer 742 c is formed using a material containingeither In or Ga or both of them. Typical examples are an In—Ga oxide (anoxide containing In and Ga), an In—Zn oxide (an oxide containing In andZn), and an In-M-Zn oxide (an oxide containing In, an element M, andZn). The element M is one or more kinds of elements selected from Al,Ti, Ga, Y, Zr, La, Ce, Nd, and Hf and has a higher strength of bondingwith oxygen than that of In.

The semiconductor layer 742 a and the semiconductor layer 742 c arepreferably formed using a material containing one or more kinds of metalelements contained in the semiconductor layer 742 b. With the use ofsuch a material, interface states are less likely to be generated at theinterface between the semiconductor layer 742 a and the semiconductorlayer 742 b and at the interface between the semiconductor layer 742 cand the semiconductor layer 742 b. Accordingly, carriers are not likelyto be scattered or captured at the interfaces, which results in animprovement in field-effect mobility of the transistor. Furthermore,variation in threshold voltage of the transistor can be reduced. Thus, asemiconductor device having favorable electrical characteristics can beobtained.

Each of the thicknesses of the semiconductor layers 742 a and 742 c isgreater than or equal to 3 nm and less than or equal to 100 nm,preferably greater than or equal to 3 nm and less than or equal to 50nm. The thickness of the semiconductor layer 742 b is greater than orequal to 3 nm and less than or equal to 700 nm, preferably greater thanor equal to 3 nm and less than or equal to 100 nm, more preferablygreater than or equal to 3 nm and less than or equal to 50 nm.

In the case where the semiconductor layer 742 b includes an In-M-Znoxide and the semiconductor layers 742 a and 742 c each also include anIn-M-Zn oxide, the semiconductor layers 742 a and 742 c each have theatomic ratio where In:M:Zn=x₁:y₁:z₁, and the semiconductor layer 742 bhas an atomic ratio where In:M:Zn=x₂:y₂:z₂, for example. In that case,the compositions of the semiconductor layers 742 a, 742 c, and 742 b canbe determined so that y₁/x₁ is larger than y₂/x₂. It is preferable thatthe compositions of the semiconductor layers 742 a, 742 c, and 742 b bedetermined so that y₁/x₁ is 1.5 times or more as large as y₂/x₂. It ismore preferable that the compositions of the semiconductor layers 742 a,742 c, and 742 b be determined so that y₁/x₁ is twice or more as largeas y₂/x₂. It is more preferable that the compositions of thesemiconductor layers 742 a, 742 c, and 742 b be determined so that y₁/x₁is three times or more as large as y₂/x₂. It is preferable that y₁ begreater than or equal to x₁ because the transistor can have stableelectrical characteristics. However, when y₁ is three times or more aslarge as x₁, the field-effect mobility of the transistor is reduced;accordingly, y₁ is preferably smaller than three times x₁. When thesemiconductor layer 742 a and the semiconductor layer 742 c have theabove compositions, the semiconductor layer 742 a and the semiconductorlayer 742 c can each be a layer in which oxygen vacancies are lesslikely to be generated than in the semiconductor layer 742 b.

In the case where the semiconductor layer 742 a and the semiconductorlayer 742 c each include an In-M-Zn oxide, the percentages of In and theelement M, not taking Zn and O into consideration, are preferably asfollows: the percentage of In is lower than 50 atomic % and thepercentage of the element M is higher than or equal to 50 atomic %. Thepercentages of In and the element Mare more preferably as follows: thepercentage of In is lower than 25 atomic % and the percentage of theelement M is higher than or equal to 75 atomic %. In the case where thesemiconductor layer 742 b includes an In-M-Zn oxide, the percentages ofIn and the element M, not taking Zn and O into consideration, arepreferably as follows: the percentage of In is higher than or equal to25 atomic % and the percentage of the element M is lower than 75 atomic%. The percentages of In and the element M are more preferably asfollows: the percentage of In is higher than or equal to 34 atomic % andthe percentage of the element M is lower than 66 atomic %.

For example, an In—Ga—Zn oxide that is formed using a target having anatomic ratio of In:Ga:Zn=1:3:2, 1:3:4, 1:3:6, 1:6:4, or 1:9:6, an In—Gaoxide that is formed using a target having an atomic ratio of In:Ga=1:9,or gallium oxide can be used for each of the semiconductor layers 742 aand 742 c containing In or Ga. Furthermore, an In—Ga—Zn oxide that isformed using a target having an atomic ratio of In:Ga:Zn=3:1:2, 1:1:1,5:5:6, or 4:2:4.1 can be used for the semiconductor layer 742 b. Notethat the atomic ratio of each of the semiconductor layers 742 a, 742 b,and 742 c may vary within a range of ±20% of any of the above-describedatomic ratios as an error.

To give stable electrical characteristics to the transistor includingthe semiconductor layer 742 b, it is preferable that impurities andoxygen vacancies in the semiconductor layer 742 b be reduced to obtain ahighly purified oxide semiconductor layer and accordingly thesemiconductor layer 742 b can be regarded as an intrinsic orsubstantially intrinsic oxide semiconductor layer. Furthermore, it ispreferable that at least the channel formation region of thesemiconductor layer 742 b be regarded as an intrinsic or substantiallyintrinsic oxide semiconductor layer.

Note that the substantially intrinsic oxide semiconductor layer refersto an oxide semiconductor layer in which the carrier density is higherthan or equal to 1×10⁻⁹/cm³ and lower than 8×10¹¹/cm³, preferably lowerthan 1×10¹¹/cm³, more preferably lower than 1×10¹⁰/cm³.

FIGS. 85A to 85C illustrate an example of the structure of a transistorusing an oxide semiconductor for the semiconductor layer 742. In atransistor 822 illustrated in FIGS. 85A to 85C, the semiconductor layer742 b is formed over the semiconductor layer 742 a. The transistor 822is a kind of bottom-gate transistor including a back gate electrode.FIG. 85A is a top view of the transistor 822. FIG. 85B is across-sectional view (in the channel length direction) taken along thedashed-dotted line X1-X2 in FIG. 85A. FIG. 85C is a cross-sectional view(in the channel width direction) taken along the dashed-dotted lineY1-Y2 in FIG. 85A.

The electrode 723 provided over the insulating layer 729 is electricallyconnected to the electrode 746 through an opening 747 a and an opening747 b provided in the insulating layers 726, 728, and 729. Thus, thesame potential is supplied to the electrodes 723 and 746. Furthermore,either or both of the openings 747 a and 747 b may be omitted. In thecase where both the openings 747 a and 747 b are omitted, differentpotentials can be supplied to the electrodes 723 and 746.

[Energy Band Structure of Oxide Semiconductor]

The function and effect of the semiconductor layer 742 that is a stackedlayer including the semiconductor layers 742 a, 742 b, and 742 c aredescribed with an energy band structure diagram shown in FIGS. 89A and89B. FIG. 89A is the energy band structure diagram showing a portionalong the dashed-dotted line D1-D2 in FIG. 84B. FIG. 89A illustrates theenergy band structure of a channel formation region of the transistor850.

In FIG. 89A, Ec882, Ec883 a, Ec883 b, Ec883 c, and Ec886 indicate theenergy of the conduction band minimum of the insulating layer 772, thesemiconductor layer 742 a, the semiconductor layer 742 b, thesemiconductor layer 742 c, and the insulating layer 726, respectively.

Here, a difference in energy between the vacuum level and the conductionband minimum (the difference is also referred to as “electron affinity”)corresponds to a value obtained by subtracting an energy gap from adifference in energy between the vacuum level and the valence bandmaximum (the difference is also referred to as an ionization potential).Note that the energy gap can be measured with a spectroscopicellipsometer (e.g., UT-300 by HORIBA JOBIN YVON S.A.S.). The energydifference between the vacuum level and the valence band maximum can bemeasured with an ultraviolet photoelectron spectroscopy (UPS) device(e.g., VersaProbe by ULVAC-PHI, Inc.).

Note that an In—Ga—Zn oxide which is formed using a target having anatomic ratio of In:Ga:Zn=1:3:2 has an energy gap of approximately 3.5 eVand an electron affinity of approximately 4.5 eV. An In—Ga—Zn oxidewhich is formed using a target having an atomic ratio of In:Ga:Zn=1:3:4has an energy gap of approximately 3.4 eV and an electron affinity ofapproximately 4.5 eV. An In—Ga—Zn oxide which is formed using a targethaving an atomic ratio of In:Ga:Zn=1:3:6 has an energy gap ofapproximately 3.3 eV and an electron affinity of approximately 4.5 eV.An In—Ga—Zn oxide which is formed using a target having an atomic ratioof In:Ga:Zn=1:6:2 has an energy gap of approximately 3.9 eV and anelectron affinity of approximately 4.3 eV. An In—Ga—Zn oxide which isformed using a target having an atomic ratio of In:Ga:Zn=1:6:8 has anenergy gap of approximately 3.5 eV and an electron affinity ofapproximately 4.4 eV. An In—Ga—Zn oxide which is formed using a targethaving an atomic ratio of In:Ga:Zn=1:6:10 has an energy gap ofapproximately 3.5 eV and an electron affinity of approximately 4.5 eV.An In—Ga—Zn oxide which is formed using a target having an atomic ratioof In:Ga:Zn=1:1:1 has an energy gap of approximately 3.2 eV and anelectron affinity of approximately 4.7 eV. An In—Ga—Zn oxide which isformed using a target having an atomic ratio of In:Ga:Zn=3:1:2 has anenergy gap of approximately 2.8 eV and an electron affinity ofapproximately 5.0 eV.

Since the insulating layer 772 and the insulating layer 726 areinsulators, Ec882 and Ec886 are closer to the vacuum level (have asmaller electron affinity) than Ec883 a, Ec883 b, and Ec883 c.

Ec883 a is closer to the vacuum level than Ec883 b. Specifically, Ec833a is preferably closer to the vacuum level than Ec883 b by 0.05 eV ormore, 0.07 eV or more, 0.1 eV or more, or 0.15 eV or more and 2 eV orless, 1 eV or less, 0.5 eV or less, or 0.4 eV or less.

Ec883 c is closer to the vacuum level than Ec883 b. Specifically, Ec883c is preferably closer to the vacuum level than Ec883 b by 0.05 eV ormore, 0.07 eV or more, 0.1 eV or more, or 0.15 eV or more and 2 eV orless, 1 eV or less, 0.5 eV or less, or 0.4 eV or less.

In the vicinity of the interface between the semiconductor layer 742 aand the semiconductor layer 742 b and the vicinity of the interfacebetween the semiconductor layer 742 b and the semiconductor layer 742 c,mixed regions are formed; thus, the energy of the conduction bandminimum continuously changes. In other words, no state or few statesexist at these interfaces.

Accordingly, electrons transfer mainly through the semiconductor layer742 b in the stacked-layer structure having the above energy bandstructure. Therefore, even when states exist at the interface betweenthe semiconductor layer 742 a and the insulating layer 724 or at theinterface between the semiconductor layer 742 c and the insulating layer726, the states hardly influence the transfer of the electrons. Inaddition, the states do not exist or hardly exist at the interfacebetween the semiconductor layer 742 a and the semiconductor layer 742 band at the interface between the semiconductor layer 742 c and thesemiconductor layer 742 b; thus, transfer of electrons is not prohibitedin the regions. Consequently, a high field-effect mobility can beobtained in the transistor having the stacked-layer structure of theabove oxide semiconductors.

Note that although trap states 890 due to impurities or defects might beformed in the vicinity of the interface between the semiconductor layer742 a and the insulating layer 772 and in the vicinity of the interfacebetween the semiconductor layer 742 c and the insulating layer 726 asshown in FIG. 89A, the semiconductor layer 742 b can be apart from thetrap states owing to the existence of the semiconductor layer 742 a andthe semiconductor layer 742 c.

In particular, in the transistor described in this embodiment, an uppersurface and a side surface of the semiconductor layer 742 b are incontact with the semiconductor layer 742 c, and a lower surface of thesemiconductor layer 742 b is in contact with the semiconductor layer 742a. In this manner, the semiconductor layer 742 b is covered by thesemiconductor layers 742 a and 742 c, whereby the influence of the trapstates can further be reduced.

Note that in the case where the energy difference between Ec883 a andEc883 b or between Ec883 c and E883 b is small, electrons in thesemiconductor layer 742 b might reach the trap states by passing overthe energy difference. The electrons are captured by the trap states,which generates negative fixed electric charge at the interface with theinsulating layer, causing the threshold voltage of the transistor to beshifted in the positive direction.

Therefore, each of the energy differences between Ec883 a and Ec883 band between Ec883 c and Ec883 b is set to be greater than or equal to0.1 eV, preferably greater than or equal to 0.15 eV, in which case avariation in the threshold voltage of the transistor can be reduced andthe transistor can have favorable electrical characteristics.

Each of the band gaps of the semiconductor layer 742 a and thesemiconductor layer 742 c is preferably wider than that of thesemiconductor layer 742 b.

FIG. 89B is the energy band structure diagram showing a portion alongthe dashed-dotted line D3-D4 in FIG. 85B. FIG. 89B shows the energy bandstructure of a channel formation region of the transistor 822.

In FIG. 89B, Ec887 represents the energy of the conduction band minimumof the insulating layer 728. The semiconductor layer 742 is formed usingtwo layers, the semiconductor layers 742 a and 742 b; thus, thetransistor can be manufactured with improved productivity. Since thesemiconductor layer 742 c is not provided, the transistor including thetwo semiconductor layers is easily affected by the trap states 890 butcan have a higher field-effect mobility than a transistor including onesemiconductor layer as the semiconductor layer 742.

In accordance with one embodiment of the present invention, a transistorwith a small variation in electrical characteristics can be provided.Accordingly, a semiconductor device with a small variation in electricalcharacteristics can be provided. In accordance with one embodiment ofthe present invention, a transistor with high reliability can beprovided. Accordingly, a semiconductor device with high reliability canbe provided.

An oxide semiconductor has an energy gap as wide as 3.0 eV or more and ahigh visible-light transmissivity. In a transistor obtained byprocessing an oxide semiconductor under appropriate conditions, theoff-state current at ambient temperature (e.g., 25° C.) can be lowerthan or equal to 100 zA (1×10⁻¹⁹ A), lower than or equal to 10 zA(1×10⁻²⁰ A), and further lower than or equal to 1 zA (1×10⁻²¹ A).Therefore, a semiconductor device with low power consumption can beachieved.

In accordance with one embodiment of the present invention, a transistorwith low power consumption can be provided. Accordingly, a displayelement or a semiconductor device such as a display device with lowpower consumption can be provided. Moreover, a display element or asemiconductor device such as a display device with high reliability canbe provided.

The transistor 850 illustrated in FIGS. 84A to 84C is described again.When the semiconductor layer 742 b is provided over the projection ofthe insulating layer 772, the side surface of the semiconductor layer742 b can also be covered with the electrode 743. Thus, the transistor850 has a structure in which the semiconductor layer 742 b can beelectrically surrounded by an electric field of the electrode 743. Sucha structure of a transistor in which a semiconductor layer in which achannel is formed is electrically surrounded by an electric field of aconductive film is called a surrounded channel (s-channel) structure. Atransistor with an s-channel structure is referred to as an s-channeltransistor.

In an s-channel structure, a channel can be formed in the whole (bulk)of the semiconductor layer 742 b. In an s-channel structure, the draincurrent of the transistor can be increased, so that a larger amount ofon-state current can be obtained. Furthermore, the entire channelformation region of the semiconductor layer 742 b can be depleted by anelectric field of the electrode 743. Accordingly, the off-state currentof the transistor with an s-channel structure can further be reduced.

When the projection of the insulating layer 772 is increased in heightand the channel width is shortened, the effects of an s-channelstructure to increase the on-state current and reduce the off-statecurrent can be enhanced. Part of the semiconductor layer 742 a exposedat the time of forming the semiconductor layer 742 b may be removed. Inthat case, the side surfaces of the semiconductor layer 742 a and thesemiconductor layer 742 b may be aligned with each other.

As in a transistor 851 illustrated in FIGS. 86A to 86C, the electrode723 may be provided below the semiconductor layer 742 with an insulatinglayer provided therebetween. FIG. 86A is a top view of the transistor851. FIG. 86B is a cross-sectional view taken along the dashed-dottedline X1-X2 in FIG. 86A. FIG. 86C is a cross-sectional view taken alongthe dashed-dotted line Y1-Y2 in FIG. 86A.

As in a transistor 852 illustrated in FIGS. 87A to 87C, an insulatinglayer 775 may be provided over the electrode 743, and a layer 725 may beprovided over the insulating layer 775. FIG. 87A is a top view of thetransistor 852. FIG. 87B is a cross-sectional view taken along thedashed-dotted line X1-X2 in FIG. 87A. FIG. 87C is a cross-sectional viewtaken along the dashed-dotted line Y1-Y2 in FIG. 87A.

Although the layer 725 is provided over the insulating layer 775 inFIGS. 87A to 87C, the layer 725 may be provided over the insulatinglayer 728 or 729. The layer 725 formed using a material with alight-blocking property can prevent a variation in characteristics, adecrease in reliability, or the like of the transistor caused by lightirradiation. When the layer 725 is formed at least larger than thesemiconductor layer 742 b such that the semiconductor layer 742 b iscovered with the layer 725, the above effects can be improved. The layer725 can be formed using an organic material, an inorganic material, or ametal material. In the case where the layer 725 is formed using aconductive material, voltage can be supplied to the layer 725 or thelayer 725 may be brought into an electrically floating state.

FIGS. 88A to 88C illustrate an example of a transistor with an s-channelstructure. A transistor 848 illustrated in FIGS. 88A to 88C has almostthe same structure as the transistor 847. In the transistor 848, thesemiconductor layer 742 is formed over a projection of the insulatinglayer 772. The transistor 848 is a type of top-gate transistor includinga back gate electrode. FIG. 88A is a top view of the transistor 848.FIG. 88B is a cross-sectional view taken along the dashed-dotted lineX1-X2 in FIG. 88A. FIG. 88C is a cross-sectional view taken along thedashed-dotted line Y1-Y2 in FIG. 88A.

The electrode 744 a provided over the insulating layer 729 iselectrically connected to the semiconductor layer 742 through an opening747 c formed in the insulating layers 726, 728, and 729. The electrode744 b provided over the insulating layer 729 is electrically connectedto the semiconductor layer 742 through an opening 747 d formed in theinsulating layers 726, 728, and 729.

The electrode 743 provided over the insulating layer 726 is electricallyconnected to the electrode 723 through an opening 747 a and an opening747 b formed in the insulating layers 726 and 772. Accordingly, the samepotential is supplied to the electrodes 746 and 723. Furthermore, eitheror both of the openings 747 a and 747 b may be omitted. In the casewhere both the openings 747 a and 747 b are omitted, differentpotentials can be supplied to the electrodes 723 and 746.

Note that the semiconductor layer in the transistor with an s-channelstructure is not limited to include an oxide semiconductor.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Embodiment 4

In this embodiment, a display module and electronic devices that includethe display device or the touch panel of one embodiment of the presentinvention will be described with reference to FIG. 90 , FIGS. 91A to91H, and FIGS. 92A and 92B.

In a display module 8000 illustrated in FIG. 90 , a touch panel 8004connected to an FPC 8003, a frame 8009, a printed board 8010, and abattery 8011 are provided between an upper cover 8001 and a lower cover8002.

The touch panel of one embodiment of the present invention can be usedfor the touch panel 8004, for example.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the size of the touchpanel 8004.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and may be formed so as to overlap with a display panel. Acounter substrate (sealing substrate) of the touch panel 8004 can have atouch panel function. A photosensor may be provided in each pixel of thetouch panel 8004 so that an optical touch panel can be obtained.

In the case of a transmissive liquid crystal element, a backlight 8007may be provided as illustrated in FIG. 90 . The backlight 8007 includesa light source 8008. Note that although a structure in which the lightsource 8008 is provided over the backlight 8007 is illustrated in FIG.90 , one embodiment of the present invention is not limited to thisstructure. For example, a structure in which the light source 8008 isprovided at an end portion of the backlight 8007 and a light diffusionplate is further provided may be employed. Note that the backlight 8007needs not be provided in the case where a self-luminous light-emittingelement such as an organic EL element is used or in the case where areflective panel or the like is employed.

The frame 8009 protects the touch panel 8004 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 can alsofunction as a radiator plate.

The printed board 8010 is provided with a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying electric power to the powersupply circuit, an external commercial power source or a power sourceusing the battery 8011 provided separately may be used. The battery 8011can be omitted in the case of using a commercial power source.

The touch panel 8004 can be additionally provided with a component suchas a polarizing plate, a retardation plate, or a prism sheet.

FIGS. 91A to 91H and FIGS. 92A and 92B illustrate electronic devices.These electronic devices can each include a housing 5000, a displayportion 5001, a speaker 5003, an LED lamp 5004, operation keys 5005(including a power switch or an operation switch), a connection terminal5006, a sensor 5007 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), a microphone 5008, and the like.

FIG. 91A illustrates a mobile computer, which can include a switch 5009,an infrared port 5010, and the like in addition to the above components.FIG. 91B illustrates a portable image reproducing device provided with arecording medium (e.g., a DVD reproducing device), which can include asecond display portion 5002, a recording medium reading portion 5011,and the like in addition to the above components. FIG. 91C illustrates atelevision device, which can include a stand 5012 and the like inaddition to the above components. The television device can be operatedby an operation switch of the housing 5000 or a separate remotecontroller 5013. With operation keys of the remote controller 5013,channels and volume can be controlled, and images displayed on thedisplay portion 5001 can be controlled. The remote controller 5013 maybe provided with a display portion for displaying data output from theremote controller 5013. FIG. 91D illustrates a portable game machine,which can include the recording medium reading portion 5011 and the likein addition to the above components. FIG. 91E illustrates a digitalcamera that has a television reception function and can include anantenna 5014, a shutter button 5015, an image receiving portion 5016,and the like in addition to the above components. FIG. 91F illustrates aportable game machine, which can include the second display portion5002, the recording medium reading portion 5011, and the like inaddition to the above components. FIG. 91G illustrates a portabletelevision receiver, which can include a charger 5017 capable oftransmitting and receiving signals, and the like in addition to theabove components. FIG. 91H illustrates a wrist-watch-type informationterminal, which can include a band 5018, a clasp 5019, and the like inaddition to the above components. The display portion 5001 mounted inthe housing 5000 also serving as a bezel includes a non-rectangulardisplay region. The display portion 5001 can display an icon 5020indicating time, another icon 5021, and the like. FIG. 92A illustrates adigital signage. FIG. 92B illustrates a digital signage mounted on acylindrical pillar.

The electronic devices illustrated in FIGS. 91A to 91H and FIGS. 92A and92B can have a variety of functions, for example, a function ofdisplaying a variety of information (e.g., a still image, a movingimage, and a text image) on a display portion, a touch panel function, afunction of displaying a calendar, date, time, and the like, a functionof controlling processing with a variety of software (programs), awireless communication function, a function of being connected to avariety of computer networks with a wireless communication function, afunction of transmitting and receiving a variety of data with a wirelesscommunication function, and a function of reading a program or datastored in a recording medium and displaying the program or data on adisplay portion. Furthermore, the electronic device including aplurality of display portions can have a function of displaying imageinformation mainly on one display portion while displaying textinformation mainly on another display portion, a function of displayinga three-dimensional image by displaying images where parallax isconsidered on a plurality of display portions, or the like. Furthermore,the electronic device including an image receiving portion can have afunction of photographing a still image, a function of photographing amoving image, a function of automatically or manually correcting aphotographed image, a function of storing a photographed image in arecording medium (an external recording medium or a recording mediumincorporated in the camera), a function of displaying a photographedimage on a display portion, or the like. Note that the functions of theelectronic devices illustrated in FIGS. 91A to 91H and FIGS. 92A and 92Bare not limited thereto, and the electronic devices can have a varietyof functions.

The electronic devices in this embodiment each include a display portionfor displaying some kind of information. The touch panel of oneembodiment of the present invention can be used for the display portion.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

EXPLANATION OF REFERENCE

10: touch panel, 11: substrate, 12: substrate, 13: FPC, 14: conductivelayer, 15: connection layer, 20: liquid crystal element, 21: conductivelayer, 22: conductive layer, 23: liquid crystal, 31: coloring layer, 41:conductive layer, 41 a: conductive layer, 41 b: conductive layer, 51:pixel electrode, 52: common electrode, 55: sensor electrode, 56: sensorelectrode, 57: wiring, 61: wiring, 62: wiring, 63: transistor, 64:liquid crystal element, 65_1: block, 65_2: block, 66: wiring, 71:wiring, 71_1: wiring, 71_2: wiring, 72: wiring, 72_1: wiring, 72_2:wiring, 81: source line, 82: source line, 83: source line, 84: sourceline, 85: gate line, 86: gate line, 87: gate line, 88: gate line, 100:display device, 151: connection layer, 201: transistor, 202:light-emitting element, 203: transistor, 206: connection portion, 207:conductive layer, 208: liquid crystal element, 209: connection layer,211: insulating layer, 212: insulating layer, 213: insulating layer,214: insulating layer, 215: insulating layer, 216: spacer, 217:insulating layer, 231: coloring layer, 232: light-blocking layer, 251:conductive layer, 252: conductive layer, 253: liquid crystal, 254:insulating layer, 255: insulating layer, 262: region, 263: region, 281:gate electrode, 282: gate electrode, 283: gate electrode, 284: gateelectrode, 285: drain electrode, 310: touch panel, 311: conductivelayer, 321: conductive layer, 322: EL layer, 323: conductive layer, 324:optical adjustment layer, 331: conductive layer, 332: conductive layer,335: conductive layer, 341: conductive layer, 351: conductive layer,352: conductive layer, 371: substrate, 372: substrate, 373: FPC, 373 a:FPC, 373 b: FPC, 374: IC, 381: display portion, 382: driver circuit,383: wiring, 384: driver circuit, 385: connection portion, 386:connector, 401: conductive layer, 402: conductive layer, 404: conductivelayer, 405: conductive layer, 411 a: conductive layer, 411 a_1:conductive layer, 411 aa: conductive layer, 411 b: conductive layer, 411b_1: conductive layer, 411 bb: conductive layer, 411 c: conductivelayer, 412 a: conductive layer, 412 aa: conductive layer, 412 b:conductive layer, 412 bb: conductive layer, 412 c: conductive layer,500A: display device, 500B: display device, 510: pixel portion, 511:pixel, 520_1: gate driver, 520_2: gate driver, 530: source driver, 531:TAB tape, 532_k: source driver IC, 532_1: source driver IC, 601: pulsevoltage output circuit, 602: current sensing circuit, 603: capacitor,621: electrode, 622: electrode, 723: electrode, 724 a: electrode, 724 b:electrode, 725: layer, 726: insulating layer, 727: insulating layer,728: insulating layer, 729: insulating layer, 741: insulating layer,742: semiconductor layer, 742 a: semiconductor layer, 742 b:semiconductor layer, 742 c: semiconductor layer, 743: electrode, 744 a:electrode, 744 b: electrode, 746: electrode, 747 a: opening, 747 b:opening, 747 c: opening, 747 d: opening, 755: impurity, 771: substrate,772: insulating layer, 775: insulating layer, 810: transistor, 811:transistor, 820: transistor, 821: transistor, 822: transistor, 825:transistor, 830: transistor, 831: transistor, 834: transistor, 840:transistor, 841: transistor, 842: transistor, 843: transistor, 844:transistor, 845: transistor, 846: transistor, 847: transistor, 848:transistor, 850: transistor, 851: transistor, 852: transistor, 882: Ec,883 a: Ec, 883 b: Ec, 883 c: Ec, 886: Ec, 887: Ec, 890: trap state,5000: housing, 5001: display portion, 5002: display portion, 5003:speaker, 5004: LED lamp, 5005: operation key, 5006: connection terminal,5007: sensor, 5008: microphone, 5009: switch, 5010: infrared port, 5011:recording medium reading portion, 5012: stand, 5013: remote controller,5014: antenna, 5015: shutter button, 5016: image receiving portion,5017: charger, 5018: band, 5019: clasp, 5020: icon, 5021: icon, 8000:display module, 8001: upper cover, 8002: lower cover, 8003: FPC, 8004:touch panel, 8006: display panel, 8007: backlight, 8008: light source,8009: frame, 8010: printed board, 8011: battery

This application is based on Japanese Patent Application serial no.2015-066887 filed with Japan Patent Office on Mar. 27, 2015 and JapanesePatent Application serial no. 2015-081398 filed with Japan Patent Officeon Apr. 13, 2015, the entire contents of which are hereby incorporatedby reference.

The invention claimed is:
 1. A display device comprising: a firstsubstrate; a second substrate; a liquid crystal element using a fringefield switching mode, the liquid crystal element comprising a pixelelectrode comprising a slit; a transistor comprising a polycrystallinesemiconductor in a channel formation region; a first conductive layer; asecond conductive layer; a third conductive layer; a touch sensor; asource signal line electrically connected to the transistor; and an FPC,wherein the first conductive layer comprises a region functioning as oneelectrode of the touch sensor, wherein the pixel electrode is providedover and in contact with an insulating layer, wherein the firstconductive layer is electrically connected to the second conductivelayer through a first contact hole in the insulating layer, wherein thepixel electrode is electrically connected to one of a source and a drainof the transistor through a second contact hole in the insulating layer,wherein the second conductive layer overlaps with the source signalline, wherein the FPC is electrically connected to the third conductivelayer, and wherein the first conductive layer, the second conductivelayer, the third conductive layer, and the liquid crystal element areprovided between the first substrate and the second substrate.
 2. Thedisplay device according to claim 1, wherein the first conductive layer,the second conductive layer, and the third conductive layer are providedover the first substrate.
 3. The display device according to claim 1,further comprising a fourth conductive layer over the second conductivelayer, wherein the fourth conductive layer is provided over and incontact with the insulating layer.
 4. The display device according toclaim 1, further comprising a coloring layer over the pixel electrode.5. The display device according to claim 1, wherein the first conductivelayer is in contact with the insulating layer.
 6. The display deviceaccording to claim 1, wherein the source signal line is configured tosupply a video signal to a pixel in the display device.
 7. A displaydevice comprising: a first substrate; a second substrate; a liquidcrystal element using a fringe field switching mode, the liquid crystalelement comprising a pixel electrode comprising a slit; a transistorcomprising silicon in a channel formation region; a first conductivelayer; a second conductive layer; a third conductive layer; a touchsensor; a source signal line electrically connected to the transistor;and an FPC, wherein the first conductive layer comprises a regionfunctioning as one electrode of the touch sensor, wherein the pixelelectrode is provided over and in contact with an insulating layer,wherein the first conductive layer is electrically connected to thesecond conductive layer through a first contact hole in the insulatinglayer, wherein the pixel electrode is electrically connected to one of asource and a drain of the transistor through a second contact hole inthe insulating layer, wherein the second conductive layer overlaps withthe source signal line, wherein the FPC is electrically connected to thethird conductive layer, and wherein the first conductive layer, thesecond conductive layer, the third conductive layer, and the liquidcrystal element are provided between the first substrate and the secondsubstrate.
 8. The display device according to claim 7, wherein the firstconductive layer, the second conductive layer, and the third conductivelayer are provided over the first substrate.
 9. The display deviceaccording to claim 7, further comprising a fourth conductive layer overthe second conductive layer, wherein the fourth conductive layer isprovided over and in contact with the insulating layer.
 10. The displaydevice according to claim 7, further comprising a coloring layer overthe pixel electrode.
 11. The display device according to claim 7,wherein the first conductive layer is in contact with the insulatinglayer.
 12. The display device according to claim 7, wherein the sourcesignal line is configured to supply a video signal to a pixel in thedisplay device.
 13. A display device comprising: a first substrate; asecond substrate; a liquid crystal element using a fringe fieldswitching mode, the liquid crystal element comprising a pixel electrodecomprising a slit; a transistor electrically connected to the liquidcrystal element; a first conductive layer; a second conductive layer; athird conductive layer; a touch sensor; a source signal lineelectrically connected to the transistor; and an FPC, wherein the firstconductive layer comprises a region functioning as one electrode of thetouch sensor, wherein the pixel electrode is provided over and incontact with an insulating layer, wherein the first conductive layer iselectrically connected to the second conductive layer through a firstcontact hole in the insulating layer, wherein the pixel electrode iselectrically connected to one of a source and a drain of the transistorthrough a second contact hole in the insulating layer, wherein thesecond conductive layer overlaps with the source signal line, whereinthe FPC is electrically connected to the third conductive layer, andwherein the first conductive layer, the second conductive layer, thethird conductive layer, and the liquid crystal element are providedbetween the first substrate and the second substrate.
 14. The displaydevice according to claim 13, wherein the first conductive layer, thesecond conductive layer, and the third conductive layer are providedover the first substrate.
 15. The display device according to claim 13,further comprising a fourth conductive layer over the second conductivelayer, wherein the fourth conductive layer is provided over and incontact with the insulating layer.
 16. The display device according toclaim 13, further comprising a coloring layer over the pixel electrode.17. The display device according to claim 13, wherein the firstconductive layer is in contact with the insulating layer.
 18. Thedisplay device according to claim 13, wherein the source signal line isconfigured to supply a video signal to a pixel in the display device.